Hello, sorry for the late reply,
On the flight I took the image I had reached cruise level and had a speed of about 330 as shown on the autopilot, due to the stall it dropped, so you'r right on that.
Also just to confirm, I need to make sure the speed stays below 280kt and I'm below the red line as well as that the PFD indicates below 0.82 for my next flight, right?
If so I am quite sure it's the solution as it explains
Why it happens near descent and cruise timing as it's the time the engines have enough time to reach top speed and for damage and structure damage to occur.
It also explains why it happened 1 out of 2 times, as the only time it didn't happen was on a rather short flight and the speed didn't have enough time to reach 330kts or above 280kts and also it didn't have enough damage from overspeeding to be out of my controls.
I thought the speed limit was 350kts as only then the alarm for it would occur on the B737 on the Zibo mod and on the default and also didn't really expected it to be that realistic for strucure damage to occur as well as the loss of control. Will try it out on my next flight and get back soon, thanks for your help!