My brother called me regarding a question with his new P229c, apparently the decocker isn’t functioning without a round in the chamber. Is that normal? I checked online and couldn’t find anything, hoping y’all could help.

No that’s not normal. The decocker serves to decock a cocked hammer and the chamber doesn’t need to be loaded to cock or decock the hammer.

Is the slide not fully in battery, by chance?

Certainly not normal and there is no connection that I am aware of.

Was there ever a resolution to this? Seems like an odd problem as I can see no mechanical correlation between the decocker and a chambered round. There has to be some other factor at play here...

No offense but this sounds like operator error.

Did he change the grips?

OP, can you provide any more detailed information? As others have stated, it's not normal and I there should be no relationship between de-cocking and a round in the chamber.