I just wanted to weigh in because I am a sleep tech but a lot of sleep labs are un-accredited and some of the techs in the industry really are terrible at their jobs. There's been a big push to get everyone registered and certified nationally but you might want to make sure the place you went to have your study and your sleep doctor was ABSM certified and the doctor an ABSM diplomate or some of your issues might be the machine not being calibrated properly. There used to be a lot of doctors that weren't board certified in sleep that ran their own un-accredited sleep labs and would put everyone on auto PAPs instead of actually setting the devices because the reimbursement for sleep studies used to be extremely high.
That being said my only other comment is because kava is a sedative it most likely affects your muscle patency and taking it would make your obstructive sleep apnea more acute which means your CPAP might require a higher pressure when taking it. I'd also assume, like other sedatives, that it most likely significantly affects your sleep staging which can be either a good or a bad thing, most sedatives are REM-supressants. It's entirely possible you are experiencing more lucid/vivid dreaming on it because your OSA is worse in REM while taking kava and you are actually having apneas/microarousals which is why you are semi-concious and remembering your dreams. There doesn't really seem to be much research on it and sleep from what I can tell. I'll ask the doctors here what they think of it next time I run into them but you should always at least ask a physician before taking something like that especially for drug interactions.