Hmm. What version of IPB? Have you tried running a search reindex? That can sometimes fix search sync issues.
I'm sorry upgrades keep breaking things, but there's little I can do to prevent that. I wish IPS kept a more stable framework, but the fact of the matter is they're obligated to add features/fix bugs, and their framework and chosen development/release cycle means we're at their mercy for keeping things compatible. All we can do is wait for the updates, see what broke, and fix as needed. I've always patched promptly when upgrades broke things.
In this case, the 4.1.19 issue is actually a core bug. IPS has posted a patch, which you can apply at will to fix AT&P and other affected hooks/apps. See the first bit about 'Release Patches' here, regarding Theme.php: https://invisionpower.com/release-notes/4119-r59/
Hope that helps.