Dunning activity FM is not working

Hello Experts,

We have a custom FM which is currently attached to one of the dunning activity and which should be triggered at dunning level 50.  Whenever we are dunning a customer at dunning level 50 it’s successfully getting dunned without any error and generates the dunning notice as well but somehow that attached custom FM is not getting triggered in dunning activity run.

We have checked in production and found out that this issue is only applicable to lower environment. The configuration that we have for that Dunning procedure and dunning level is same as Production environment. Have any one of you faced this issue earlier?

Thanks,

Rahul.