Hot plug bay, strange behavior

Both my Son and I have Coolrmaster CM690 II cases with a hot swap bay
built into the top. His MB is an ASUS Z390 prime A.
Yesterday I gave him a 120 GB Kingston freshly formatted SSD to store
his Photos, He plugged it in and it wouldn't show up, I took it to my
system and it works fine in my hot plug bay
Before opening the box to check fo loose Sata cables etc, I decided to
try a few things as he hasn't used that bay for a few months, I tried 2
other SSDs with no show on both, Yet they work on mine.
Then left it plugged in and tried a cold boot, Aha, now it showed up and
I can unplug it and plug in a couple otherr drives and they all work fine.
I repeated the test 3 or 4 times withe the same results, If I boot
without a drive plugged in the bay will not as if not detected, But if I
boot with a drive in the bay the drives work as normal.
I switched Sata ports on the MB and went over the bios settings with the
same results.
As it is it works fine as long as he boots with a drive in the bay.
I suspect a problem in the bay electronics but can't even see them
without dismantling the whole top of the box, Which I don't really want
to do as long as it works OK with a drive in the bay.
Any other thoughts for me to try?

Thanks, Rene