There can be fouling issues where the suppressor joins to the barrel. It's more common in military scenarios. Sig Sauer and the Army are looking into odd wear patterns with the new M7.
The m7 just seems like a lousy idea in general beyond specific use cases. 80k psi in a suppressed gas gun burning over 40 grains of powder. Throw a vortex smart scope on it and it would take a lot for me to trust that for an important hunt much less war. Were such issues present on mk18s or mk12s? Sounds like sig issues..
Something about moisture moving ions between the different metals and causing pitting in the bore. Can't remember exactly. It was explained to me in Norwegian when I bought it.