I'm really stumped with this one, so it's time to ask for help. We are creating a new 2019 SharePoint on-prem farm, and I'm having big issues with the search. The biggest one is that it doesn't create crawled properties - or rather, it sometimes creates them and sometimes not. This is going to be a long explanation, so bear with me.
I have two farms (test and future production) and I have been testing things with both of them, so I'm sure I can repeat these issues. Both farm have at least one app, one frontend with distributed cache, and one search server.
First, I installed SP2019 and August 2020 CU on each server and created a farm. I used a setup account when installing and made sure rights are set as described in this article. Then I used SharePoint DSC to configure the farm, again using a setup account. The configuration has been the same for all iterations. There are two content sources: Local SharePoint sites and an external web page.
With the August 2020 CU, I couldn't get SharePoint to find any crawled properties from either one of those content sources. Health is good, crawl log says content is indexed, I can find it if I try to search for it. But none of the columns or website metadata appears in the crawled properties. I tried to check database rights and permisisons to web application and metadata service application, and everything looks like it's correct. I found reports that SharePoint Online's Team Sites have had trouble with crawled properties (references here and here), so I though something might be wrong with the CU. I tried installing the January 2021 CU, but it didn't fix things.
Next I nuked those two farms and reinstalled them completely. I didn't install any CU, just the original SharePoint 2019 binaries, and then configured the farm with the same script as before. Now the crawled properties appeared just like they should, so everything good so far. Note that I did no changes to the configuration and I used the same content database backups, so the only thing that changed was that the CU was left out.
Since it's not really good to be running SharePoint without any CU, I read Stefan Goßner's blog to find a CU that didn't have comments about things being broken. I chose September 2019 CU and tried to install it next. I deleted the search service and created a new one, and now one of the farms does find crawled properties, but the other one doesn't. I've been through every setting I can think of and can't find any differences between these two farms. What am I missing?
During all these tests, I noticed rights for the search service application db keep dropping as described in this blog post. Because of that I always create the search service application from Central Administration first, and then use DSC to add content sources etc. However, that hasn't helped, and the rights continue being dropped each time the administrators are changed. I always add them back in, but it doesn't change how the crawled properties work. All rights are set up like best practices say, so have no idea what is wrong.
Has anyone else had similar issues? Do you have any ideas what I could try next?