Just tested 6.x. I noticed that ModSecurity said "ModSecurity: Warning. Operator GE matched 5 at TX:inbound_anomaly_score." when I tried to add subquestions to a question of type Multiple choise. Might be worth adding a note to installation guide?
Otherwise seems good, at least by ten minutes experience.
It depends on the rules ModSecurity is using. ModSecurity itself is not blocking anything but certain rules do.
I had issues with LimeSurvey in all these years. The more JavaScript was added to prevent POST and RELOAD after each interaction with the Browser the more rules are triggered. False positives are expect when using a lot of ModSecurity rules.