scuba pro hyrdos pro bcd dump valve unscrewed in the pool

Dump valve at the top back was fully unscrewed and hanging off in the pool after a dive, making the BCD non functional. Everything was "fine" during pre-dive checks and testing all the valves. I didn't notice since it was just shallow pool work.

Can't find any internet references for this happening to anyone else.

Slightly terrified of how this could have gone in open water. Yes it's recoverable, but in combination with some other issue maybe not so much.

I will now add "check all the valves are fully screwed in" to my check, and, Im going to double check everything and the O-ring that the internet says should be there is still there because I don't remember. Had the BCD pressure tested etc about 9 months ago.