This looks not like an out of memory error, but your Zammad logfile states a net redtimeout.
The following threads might already have covered your issue:
- OTRS Import timeout
- OTRS Import won't work: StatusCode: 500 {"error":"undefined method `each' for nil:NilClass"}
If something on OTRS side is crashing, we proberbly won’t really be able to help, however, this machine is right now a blackbox to this community.
Lastly, please note that we don’t have a Zammad 3.3 image for docker-compose yet - if you built one yourself, please note that you’re running a development version, as 3.2 is considered as stable. (Even though it shouldn’t affect your above issue)