Shrink it in smaller chunks.

Google for a script to reduce it incrementally.

I'm now up to 10 failovers with no sync issues.  I'm also on CU22.

I hate to possibly jinx myself, but I've had 5 failovers with no secondaries out of sync.  I've turned on ADR for a bunch of my databases.  Maybe about 60...

You probably lack the SPN's for SQL server.  You can check them with the Microsoft tool:  https://www.microsoft.com/en-US/download/details.aspx?id=39046

The tool can even generate the commands to add the missing ones.

Maybe install the Kerberos diag tool and see if it checks out:  https://www.microsoft.com/en-US/download/details.aspx?id=39046

The SSPI error is usually associated with missing SPNs.

duplicate

Make sure your server properties/database settings/database default locations are set to the drives you expect them to be.

Bummer, I figured mine was a fluke.  Thanks for the update.

I hear you on the licensing...mine is SPLA so it is very expensive to bump up.

I applied CU21 late in July.  I had my first restarts this last weekend and both my nodes came up clean with no secondary out of sync issues.   Have you...

Login failed for user 'NT AUTHORITY\ANONYMOUS LOGON'

This usually points to Kerberos double hop issues.  Check you SPN's.

You can use this tool to check it:  https://www.microsoft.com/en-US/download/details.aspx?id=39046

<sigh>  Thanks for the update.

I can confirm I also get some out of sync even though both nodes are on the same patch level.

I'm not 100% sure, but check out Erik Darling's sp_HumanEvents.

I believe you can filter by db and username and log to a table.

The log backup doesn't align with my AG either.

Ooops, I see you already commented on our similar post

It does sound similar.  I just moved from CU18 to CU19 and am waiting to see if it helped. I am thinking about switching off auto seed before the next...