I found this thread after I had already called United about my CPAP and found out that I couldn't use OLCI. I was pist that I had to deal with a human at a bit after 4AM for my 6am flight. Went to Premier check-in at LAX with nobody in line at that time of the morning. Told the agent "I am here to get a bp, check a bag, and have you look at my CPAP".

Got my bps for my LAX-SFO-HND C-award trip, checked my big carryon spinner, and that was it. No questions from the agent, no inspection of my CPAP. There was an opportunity, I thought, for UA to ask about the CPAP when they scanned my bp at the Polaris lounge at SFO. No issue then nor when I boarded either flight. The FAs on the TPAC flight had nothing to say/do about the CPAP (which is what I fully expected given that those folks have surely seen CPAPs used on long hauls before, including. the Transcend Mini that I have been using for at least 10 years.).

Turned out that checking- in at the airport was a good idea because I figured that I might as well check my big bag while i was there. I was walking with a can and hauling that big bag around with my small carryon (with the CPAP inside) stacked on top would have been a big PITA.

No issue with the CPAP on the return HND-LAX flight. Not at check-in, boarding, or onboard when I used it again.