KJW G23 blowing all gas out / not cycling.

Already lubed it a bit, let the mag warm up a bit and try again but after 2-3 shots all the gas blows out. Sometimes I can get a few more shots out of it but then it shoots 1 BB then nothing, manually cock it then it shoots 1 more, sometimes it shoots a few more but then all the gas blows out.

We've used butane to test because stores were closed and are now on holiday. What could be wrong here?

EDIT: Actually it just shot 8-9 BBs but then all the gas came out.