HTTP: proxy error: context canceled

This is a known issue, and it has beed reported at grafana/grafana#27957, and it is due to the use of multiple queries towards a Prometheus datasource.

How the error log looks like:

...
t=2021-11-05T14:30:28+0000 lvl=eror msg="Data proxy error" logger=data-proxy-log userId=17 orgId=1 uname=xxx path=/api/datasources/proxy/4/render remote_addr=2001:xxxx:xxx:xx::xxx referer="https://<some_url>" error="http: proxy error: context canceled"
...

Solution:

The solution proposed is to change the refId to a unique value in the json, according to grafana/grafana#27957 (comment)