Report Server POST powerbi/api/powerbi/refresh/subscribe returns 404

The problem I had is why the report server is trying to make POST call to https://{servername}/powerbi/api/powerbi/refresh/subscribe at all (and it's calling multiple times frequently even when I just left the report opened for a minute or two). I didn't see this in earlier version of RS. I think this is most likely an invalid URL anyway.

The report server URL is something like https://{servername}/reports.

I know the issue is not with the connection to SSAS because I could still change the slicer selection after seeing these errors popping up in the console.

We will eventually update the report to the later version but we have tens of reports and multiple servers to maintain so when we have upgraded the RS on one Dev/UAT server, the other server might still run older RS. If the pbix is saved in newer version it won't be deployable to the older RS anymore whereas new RS is supposedly backward compatible with older version of pbix. Anyway in this case even though I tried saved the pbix in the same version as the RS version and update the report in RS (e.g. May 2020 or Sep 2020) that 404 calls to the refresh/subscribe still appear in the browser console. I haven't seen any new settings in the pbix related to the Live Query auto refresh at all so I don't think the pbix version is the issue here. The RS itself seems to be trying to be connecting to that inexistent refresh/subscribe API since the May 2020 upgrade.