I've witnessed it happening via Volanta in 2020 as well. it usually happens when the weather bugs out. I love what they've done with the plane, I just hope there's a fix for that because of right now it's a hit or miss for long haul routes.
I had the same issue flying through Romania, I have AP protection on and active sky FS on. the autopilot didn't disconnect, the plane went into heading mode by itself luckily it was on the same trajectory as the airport.