FYI : I had the same issue and read/commented on the other related threads in this forum.
Based on other people comments, I installed fw 1.22 and gave it anoter try today with various settings (1080p50 Superview, 4K25 Linear+, 1080p200 Linear+) : no issues anymore, so it really looks like it's directly related to fw 1.50.
However, when I reached out to customer service to report the issue on my camera (along with other issues such as freezes, or camera powering off automatically with 20% battery left and a "low battery" message) I was told that this issue is not related to fw 1.50, but with an 'internal' problem, unrelated to firmware.
Obviously I find it very hard to believe given the tests results I and others got, so I argued with the guy on the phone about it, but after some wait, discussing with his team, he insisted that it's the motherboard, and that the issue must have been there the whole time, just not triggered until after using the camera for some time (which is also unlikely since I wasn't able to reproduce anymore after downgrading to 1.22)
Anyway, he told me to return my gopro for an exchange, so I'm sending it tomorrow, and I'll run some tests when the new one comes in.
By this time, maybe a new firmware fixing the issue will also be available...
Last but not least I asked him about a tool to fix our messed up footage, and he said nothing is ready but did not rule it out completely, so I'm not sure if they are actually working on such a tool. I'll definitely bring it up again whenever the firmware is fixed.
I don't know if other people have been asked to return their gopro for an exchange, and I surely don't count on this too much to fix the issue, but anyway, that's where I'm at, and felt this needed to be shared. To be continued...
