Unable to Reindex - important pending server tasks could not be performed

Very strange that the Solr plugin would try to send a POST request to /solr/index.html when deleting items. What does your Search API server configuration look like, esp. the “Solr path” setting?

PS: It seems you (like many others – it's really easy to misinterpret) are confused by the "Issue tags" field. As the guidelines → state, they aren't meant for free text tags related to the issue, but only for specific categorization purposes, usually by module maintainers.
So, if you aren't sure your current usage is correct, please just leave the field empty.

Hey @drunken monkey! Here is how it looks like:

Its the same on http with port 80.

By the way I am facing exact same error on local Apache solr configs as well.

I was entering wrong path to solr core, please close this. As the issue has been resolved by fixing the path.