A correct description should have been that the O2 flow had increased over time. I can not tell what it was when recieved from Jetsam, since I didn't measure it (and it worked quite well for me). On the later dives this year the O2 level kept on rising causing me to use quite some dilutent to keep the O2 level down as well as venting out quite some O2.

After trying things further, I together with some helping hands found out that it wasn't the plastic cap keeping it from beeing depthcompensated. But instead the O2 flow had increased beyond "normal" levels.

When measured the flowmeter showed approximately 1.8 litres/ minute. This is now adjusted down to 1,0 litres per minutes.

The problem was instead that the KISS valve was quite messed up with the o-rings mounted. Problem was solved by replaceing the o-rings and cleaning the parts, and then reassemblying it.
That means, please check your KISS valve once in a while or at least once in a year.