TYPO3 Core

Hi,
I'm here on TYPO3 v11 and not yet in Composer mode. So updates are installed "oldscool" via Extension Manager from TER.
Recently some of the local admins started to have the problem, that the extension update completed successfully but the Extension Manager still showed the old version number and the update button.

Clearing caches (red lightning and from maintenance module) and rebulding the autoload information did not help. So I solved it by deleting typo3temp/var/cache manually

I saw, that the outdated version number was cached in typo3temp/var/cache/code/core/PackageManager_754b0ea6278f28297f98ea95c02913d1.php

This does NOT occur when I deactivate-update-reactivate an Extension. And it can be corrected after the fact by "turning it off and on again"

• Should this information be cached in the first place?
• Should the offending file be deleted when I "Flush TYPO3 and PHP Cache"?
• Or should I have done something differently to refresh the outdated version cache?

Also but much more gravely but more vaguely:
Since roughly the same time we saw an increase of failed Extension updates, old versions seemingly leaving behind garbage in cached php, so that TYPO3 encounters confusing PHP Errors after the update, that go away when disabling and enabling the extension again. This also only occurs when the Extension is active during update and can be avoided by turning it off beforehand.