I have an Edge 530 currently, but have not had it long enough to comment on the long-term reliability. It has been solid for the last 3 months. I previously had an Edge 520 Plus and would have similar problems as you describe every few months. I noticed lots of ANT+ (no bluetooth on the 520) dropouts for both my trainer and my on-bike power meter. I found cycling the power usually fixed it, but I, like you, lost a handful of rides as well so I feel your pain. Sometimes you can manually recover your rides by plugging in to a computer and searching the filer system of the unit.

If you have the problem after a few power cycles and/or a hard reset, I would contact Garmin. I have had success replacing wonky units for free or low cost in the past.

They all have issues. They will all piss you off enough to want to try something else from another brand. Eventually, you'll end up back where you started, only it'll be the 2020 version and not the 2015 version.