Failed to build evaluator for queries and expressions: Condition C does not exist, must be one of [A]

Hi there. Just started using grafana with prometheus and trying to make an alert for high disk space usage. I have a panel like this from node exporter full dashboard:
image
So i click “create new alert rule” for it and there all the fun starts :grin:

When i do not change anything in query:

and click preview it shows me a timeseries just fine:


The problem is when i try to change legend or literally anything in a query, it shows an error:
image

But i just want to use {{job}} for a custom legend. Error occurs whenever I touch anything in the query. Even if I just switch from timeseries to table. Even I change it to previous state. It show a chart only on first click preview. Please, help me :smiling_face_with_tear: