valve spring retainer plug was backed out- Valve dump blues

I’m using a CO2 adapter with a .177 valve ahead of a JDSairman regulator and tank. Yesterday, after about a month of trouble free shooting there was a valve dump. As soon as I moved the Breech slide off of the top hat it stopped. A few more tries and same result. Put the original tank and valve back on and there is no problem.

What could be going on?