I have the above error notification on my Google search console on some of my website pages, dailynewsng.com.ng
I was told that it may be as a result of theme errors because it wasn’t like that before.
Is there anything I need to do or it is not theme related. Or any possible options to get it fixed?
Thanks. 
This is issue affecting many news websites right now, actually since October. Google is in the midst of deprecating many news sites for spammy content — meaning, just parroting news from other sources vs originating it.
Only thing you can do is look at their examples of what is not being indexed and why.
Note many can be ignored, like removing AMP pages, they will generate errors for awhile that the linked location ignored on crawl, and only the canonical version used.
Nothing to do with the theme.
You can check to make sure your sitemap works. You can check the examples Google mentions as to why pages crawled not indexed, to see if actually relevant or not, and then you can request they validate your fixes if you made actual fixes, or if you think it’s totally an error on their part.
If it was indexing error, they make come back in a week and say “some validation failed” .. and then you need to look closer at that.
Thanks for that clarification.
Other thing to try, is check one of the pages not indexed but crawled, ‘inspect’ it in your Google panel, and click ‘request indexing’ to see what happens….
this happened big time to one of our 15 year old news portals… suddenly we had 18,000 pages “crawled not indexed.”
I feel your pain and annoyance!
