So I have been having a very similar issue (maybe the same issue). I've struggled getting indexed. DIYer here.
I finally realized in google search console last week that several of my blog articles and my Categories & Tags are not indexed. Found the error on the blog about not being in the property. So I added to the property the path to the blog itself. Today I see some indexed but not all.
In my stress, I have been trying to get info from SEO groups -- and one kind soul suggested SEMRush and actually ran a report for me. I see lots of errors -- javascript and css to which I have no clue how to fix (or even if I added them). Temporary redirect, which I don' know how I did those either.
I see a lot of 503 errors that I don't understand.
That report seems to ding me for no meta descriptions on Tags and Categories -- which I'm told I cannot do in SQP.
I have been working on low hanging fruit this morning like broken links, missing descriptions, etc -- work in progress. But I feel like there are some big errors I need to fix. I just don't know how.