I have three SLR gas blocks, two on SBR's, a 10.5" 5.56 and an 11.5" 6.8 and one on a 16" 6.8 and all get shot a fair bit, almost exclusively suppressed. I have never had an issue. I'd suggest contacting SLR, sounds like you got a dud.
[BTW, I don't bother closing the block when cleaning a rifle, but I do keep the upper right side up since solvents don't drain, run or drip up.]
And just for the "mine runs fine with a standard block" crowd, I'll reiterate that if your rifle runs reliably unsuppressed there is 100% probability it is over gassed when shot suppressed. An over gassed condition can create long term reliability and service life issues, plus there is definitely excessive gas coming into the action making for a dirtier rifle with a more stringent cleaning regimen, and more gas in the face.
JPK