TYPO3 Core

Another update:
Seems to rely on the locallang value - maybe a problem with "%"

<trans-unit id="date">
    <source>%Y-%m-%d, %H:%M</source>
</trans-unit>

This helps:

<trans-unit id="date">
    <source>Y-m-d, H:i</source>
</trans-unit>

Also CDATA helps:

<trans-unit id="date">
    <source><![CDATA[%Y-%m-%d, %H:%M]]></source>
</trans-unit>

I would try, but if I go on dev-main, I cannot login into backend any more (cache flush and db compare did not help). Problem here:

#1264023823 InvalidArgumentException
"luxletter.localhost.de-8ca9805574671b9c-table-be_sessions" is not a valid cache entry identifier.

Alex Kellner wrote in #note-5:

I would try, but if I go on dev-main, I cannot login into backend any more (cache flush and db compare did not help). Problem here:
[...]

Can you please provide a stacktrace (and optionally create a new ticket for this)? Fixing this issue seems to be a low-hanging fruit.
Please see #99276 for a bugfix.

Thx, works now as expected in 12.1.0