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 am fairly new to this forum. I was on a Phantom forum when mine were new several years ago. I also have been on a few photography forums for almost 20 years and this one is loaded with misinformation. I would recommend the OP to filter it out...