In our organization, we have three WSUS server. One serves the parent domain, while the other two serve two different sites, each from the same child domain.
Up until September 2019, all the updates we have ever gone to approve where easily found in all three WSUS server consoles. After Sep 2019, only the parent domain WSUS server can find/see .NET Framework updates as well as Adobe Flash Player updates.
Monthly Windows 10 cumulative updates as well as office and others still show up every month as usual, it (so far) is just these two types of updates that I have not seen (or been able to search via name or kb) since patch Tuesday back in October.
One of these two troublesome WSUS servers is running Windows Server 2019, the other is 2016. Both are up-to-date themselves and both are standalone (not replicas of each other since they server two different sites).