I also recently experienced a similar problem on 3 different occasions, but only since the FF6.2 update. I have well over 100 flights on my Anafi, and have been flying quads for almost 5 years, during which time I've never experienced anything like this until now. The most recent occurrence happened yesterday, the yawing was much more violent than the previous occasions, after which the drone started a very rapid, un-commanded, straight line movement to the left. Opposite control had no effect, so I initiated RTH. The machine then turned and headed back to the home spot and started to descend, but would not come below approx 30 meters. It stabilized in a hover at approximately 30 meters but would not descend, even though I had selected the "Land" command, and the "Landing" indicator box was flashing. Full descend stick had no effect. I also noticed that there was an "SD Card Full" warning, even though I was only shooting 1080/30 for about 5-6 minutes. After a minute or so of no response, I attempted to make a gentle descending spiral to the left, which the Anafi did execute and landed uneventfully.
It turned out the SD card had over 80% capacity remaining.
Prior to flying again, I re-calibrated the magnetometer and double formatted the SD card. I flew 4 good flights this morning and the machine performed flawlessly. Is there a possible glitch/interaction between the IMU and the SD card?