Hi,
you may look at my answer in the German section:
https://community.i-doit.com/topic/5282/das-suchfilterdatum-funktioniert-nach-dem-upgrade-nicht-im-benutzerdefinierten-feld.
If you have large i-doit database with (ten) thousands of objects and some object types / categories which need to be searched you have to increase the php memory.
In our php.ini we have
memory_limit = 8192M
Regards
Leo