Ive been using the Incinerator for a while now for the 10,000 EW damage achievement. The reason im using the Incinerator is because it doesnt leave permanent goo/ash piles and im unable to locate a Flamer. Since ive been using it a very common occurance is that enemies become immune to damage outside of VATS. I would say this happens to about 40-50% of all enemies I encounter.

Anyone else experiencing this?

DT?

The Incinerator does mostly fire damage, and DT doesn't protect against fire damage so that is not the problem. Celery seems to have an interesting bug.