This behavior really sounds like something is interfering with the VPS sensor, making the drone constantly believing that something is closer than 0,5m below it... & by that tries to ascend away from it.
The constant descent following a longer...
I've never cleaned them (on any of my drones). But this thing is pretty new, they shouldn't be that dirty. Plus, wouldn't both the upward and downward sensors be dirty? Oh well, I'll clean 'em anyway. Thanks.
No, it always starts when I take off and continues from there. I have to pull back to stop ascent then push forward to stop the descent. Rinse and repeat.
Thank you.