Seems, that with each new app version less credits are granted.
I was checking my data and found out:

App version 2206.07 / average runtime 3600 - 3700 seconds, 68 -70 credits per WU
App version 2207.22 / average runtime 3600 - 3650 seconds, 50 -52 credits per WU
App version 2207.23 / average runtime 2650 - 2750 seconds, 40 - 42 credits per WU

Update:
There are 2207.23 WUs that run short and some that have a longer runtime. I now see WUs completed in between 3600 to 3650 seconds and credits between 82 and 84.

Looks normal again.