With my A139 I've had issues with one card; we can't blame the cam for those, I've had some random instances of restarting/boot-looping while driving; the boot-looping was only two sequences long. In all cases the cam's beeps and/or voice let me know of the problem and only a few to several seconds of video was lost. This is as good or better than any cam other than Mobius has given me. Thus I will call the A139 reliable for the purposes of driving recording, but if you want a "mission critical" cam then you'll need to do what is done with all "mission critical" systems and add redundancy;
two is one and one is none
Which leads us to deciding what the "mission" is and what it's priorities are. For me, driving recording comes first- that is the most important aspect of a dashcam. Indeed that is why they exist in the first place, so everything else rates less important. And being less important those other aspects needn't be as perfect or as reliable to still have a good dashcam. Those who expect everything any cam does to always work perfectly aren't based in reality. These truly ARE somewhat cheap consumer-grade devices where none have ever worked perfectly in every regard and none ever will.
Getting back on topic, other than the earliest and beta FW's, the A139 has been both reliable and fully functional until the last 2 (now 3) FW's came into use. Early/beta FW's usually have issues and we can extend that to new cam designs sometimes having hardware issues in early versions.
We saw a couple months where no serious issues were spoken of, and very minimal issues with anything were noted. So what has changed since then? FW
Given the seasons, there weren't a lot of temperature extremes for the average user to encounter till recent days, but several folks did see some days hot enough to cause issues with other cams, yet no issues were found with this one. Not a perfect test but it should have discovered any major heat related issues. As the seasons continue we're going to get more experiences with this to better know if there are any heat-related issues, what those are, and what aspects of use are being affected. And as always new FW is always to be suspected to have issues and to not be trusted till proven. If new FW introduces new features or significantly expands older known-to-be-stable features you can expect some problems to arise. Even the most careful and conscientious cam manufacturer occasionally has problems with new FW versions.
Life ain't perfect and neither are dashcams
Phil