<iframe> Grafana is changing display behaviour after some time randomly

I embedded several iframes of Grafana panels without an issue.
For an unknown reason, some of these panels, randomly, are shown after a while with the whole interface. See the follwowing screenshot:

While 2 is displayed as intended, 1 is diplayed with the user interface.
These panels are coded the same. After reload the page, everything is back to ok.

  1. The time after this behaviour seems randomly to me
  2. Which panel is affected seems randomly to me

After a simple reload, everything is back to ok:

Any ideas or hints for me? Thank you