Regex replace exceeds heap limit


We have a complicated activity(Event) report generated with accounts, opportunities related to couple of custom objects. Initially, we were getting JSON heap size issue. To resolve that we removed all redundant fields from the models. The we got the new error "Regex replace exceeds heap limit ". I don,t think the issue is with the data as the user who is getting the error does not have even 50 activities created in the system. 
Has anyone encountered something like this before. 
Any help is much appreciated.


I figured out the issue. It was related to incorrect config of when to abort the condition in model. What was happening is that when there was no data in source model, it was querying all data.