Graph faulty after automatic refresh

Hi, I have a graph that looks normal, the time range is set to 24 hours and refresh after one minute.

But once the graph got refreshed, it looks ugly:

The panel source:

{
  "id": 2,
  "gridPos": {
    "h": 17,
    "w": 12,
    "x": 0,
    "y": 0
  },
  "type": "timeseries",
  "title": "Temperaturen Pluggit",
  "datasource": {
    "type": "alexanderzobnin-zabbix-datasource",
    "uid": "zATExEzRz"
  },
  "pluginVersion": "8.5.2",
  "description": "",
  "fieldConfig": {
    "defaults": {
      "custom": {
        "drawStyle": "line",
        "lineInterpolation": "smooth",
        "barAlignment": 0,
        "lineWidth": 1,
        "fillOpacity": 0,
        "gradientMode": "none",
        "spanNulls": true,
        "showPoints": "auto",
        "pointSize": 5,
        "stacking": {
          "mode": "none",
          "group": "A"
        },
        "axisPlacement": "auto",
        "axisLabel": "",
        "scaleDistribution": {
          "type": "linear"
        },
        "hideFrom": {
          "tooltip": false,
          "viz": false,
          "legend": false
        },
        "thresholdsStyle": {
          "mode": "off"
        }
      },
      "color": {
        "mode": "palette-classic"
      },
      "mappings": [],
      "thresholds": {
        "mode": "absolute",
        "steps": [
          {
            "color": "green",
            "value": null
          },
          {
            "color": "red",
            "value": 80
          }
        ]
      },
      "unit": "celsius"
    },
    "overrides": []
  },
  "options": {
    "tooltip": {
      "mode": "single",
      "sort": "none"
    },
    "legend": {
      "displayMode": "list",
      "placement": "bottom",
      "calcs": []
    }
  },
  "targets": [
    {
      "application": {
        "filter": ""
      },
      "datasource": {
        "type": "alexanderzobnin-zabbix-datasource",
        "uid": "4FnpipZRz"
      },
      "functions": [
        {
          "$$hashKey": "object:3565",
          "def": {
            "category": "Alias",
            "defaultParams": [
              "/(.*)/",
              "$1"
            ],
            "name": "replaceAlias",
            "params": [
              {
                "name": "regexp",
                "type": "string"
              },
              {
                "name": "newAlias",
                "type": "string"
              }
            ]
          },
          "params": [
            "/r4: Pluggit /",
            " "
          ],
          "text": "replaceAlias(/r4: Pluggit /,  )"
        }
      ],
      "group": {
        "filter": "Quistorpweg"
      },
      "host": {
        "filter": "r4"
      },
      "item": {
        "filter": "Pluggit Außenzuluft"
      },
      "itemTag": {
        "filter": ""
      },
      "options": {
        "disableDataAlignment": false,
        "showDisabledItems": false,
        "skipEmptyValues": false,
        "useZabbixValueMapping": false
      },
      "proxy": {
        "filter": ""
      },
      "queryType": "0",
      "refId": "A",
      "resultFormat": "time_series",
      "table": {
        "skipEmptyValues": false
      },
      "tags": {
        "filter": ""
      },
      "trigger": {
        "filter": ""
      },
      "triggers": {
        "acknowledged": 2,
        "count": true,
        "minSeverity": 3
      }
    },
    {
      "application": {
        "filter": ""
      },
      "datasource": {
        "type": "alexanderzobnin-zabbix-datasource",
        "uid": "4FnpipZRz"
      },
      "functions": [
        {
          "$$hashKey": "object:3586",
          "def": {
            "category": "Alias",
            "defaultParams": [
              "/(.*)/",
              "$1"
            ],
            "name": "replaceAlias",
            "params": [
              {
                "name": "regexp",
                "type": "string"
              },
              {
                "name": "newAlias",
                "type": "string"
              }
            ]
          },
          "params": [
            "/r4: Pluggit /",
            " "
          ],
          "text": "replaceAlias(/r4: Pluggit /,  )"
        }
      ],
      "group": {
        "filter": "Quistorpweg"
      },
      "hide": false,
      "host": {
        "filter": "r4"
      },
      "item": {
        "filter": "Pluggit Außenabluft"
      },
      "itemTag": {
        "filter": ""
      },
      "options": {
        "disableDataAlignment": false,
        "showDisabledItems": false,
        "skipEmptyValues": false,
        "useZabbixValueMapping": false
      },
      "proxy": {
        "filter": ""
      },
      "queryType": "0",
      "refId": "B",
      "resultFormat": "time_series",
      "table": {
        "skipEmptyValues": false
      },
      "tags": {
        "filter": ""
      },
      "trigger": {
        "filter": ""
      },
      "triggers": {
        "acknowledged": 2,
        "count": true,
        "minSeverity": 3
      }
    },
    {
      "application": {
        "filter": ""
      },
      "datasource": {
        "type": "alexanderzobnin-zabbix-datasource",
        "uid": "4FnpipZRz"
      },
      "functions": [
        {
          "$$hashKey": "object:3607",
          "def": {
            "category": "Alias",
            "defaultParams": [
              "/(.*)/",
              "$1"
            ],
            "name": "replaceAlias",
            "params": [
              {
                "name": "regexp",
                "type": "string"
              },
              {
                "name": "newAlias",
                "type": "string"
              }
            ]
          },
          "params": [
            "/r4: Pluggit /",
            " "
          ],
          "text": "replaceAlias(/r4: Pluggit /,  )"
        }
      ],
      "group": {
        "filter": "Quistorpweg"
      },
      "hide": false,
      "host": {
        "filter": "r4"
      },
      "item": {
        "filter": "Pluggit Raumabluft"
      },
      "itemTag": {
        "filter": ""
      },
      "options": {
        "disableDataAlignment": false,
        "showDisabledItems": false,
        "skipEmptyValues": false,
        "useZabbixValueMapping": false
      },
      "proxy": {
        "filter": ""
      },
      "queryType": "0",
      "refId": "C",
      "resultFormat": "time_series",
      "table": {
        "skipEmptyValues": false
      },
      "tags": {
        "filter": ""
      },
      "trigger": {
        "filter": ""
      },
      "triggers": {
        "acknowledged": 2,
        "count": true,
        "minSeverity": 3
      }
    },
    {
      "application": {
        "filter": ""
      },
      "datasource": {
        "type": "alexanderzobnin-zabbix-datasource",
        "uid": "4FnpipZRz"
      },
      "functions": [
        {
          "$$hashKey": "object:3628",
          "def": {
            "category": "Alias",
            "defaultParams": [
              "/(.*)/",
              "$1"
            ],
            "name": "replaceAlias",
            "params": [
              {
                "name": "regexp",
                "type": "string"
              },
              {
                "name": "newAlias",
                "type": "string"
              }
            ]
          },
          "params": [
            "/r4: Pluggit /",
            " "
          ],
          "text": "replaceAlias(/r4: Pluggit /,  )"
        }
      ],
      "group": {
        "filter": "Quistorpweg"
      },
      "hide": false,
      "host": {
        "filter": "r4"
      },
      "item": {
        "filter": "Pluggit Raumzuluft"
      },
      "itemTag": {
        "filter": ""
      },
      "options": {
        "disableDataAlignment": false,
        "showDisabledItems": false,
        "skipEmptyValues": false,
        "useZabbixValueMapping": false
      },
      "proxy": {
        "filter": ""
      },
      "queryType": "0",
      "refId": "D",
      "resultFormat": "time_series",
      "table": {
        "skipEmptyValues": false
      },
      "tags": {
        "filter": ""
      },
      "trigger": {
        "filter": ""
      },
      "triggers": {
        "acknowledged": 2,
        "count": true,
        "minSeverity": 3
      }
    }
  ]
}

Any help is appreciated,

Grafana 8.5.2 on Raspbian 10.

Rainer