Playerdata gets reset to an old version when updating to 1.16.

Whenever I update a 1.15.2 world to 1.16 release candidate 1, my playerdata gets reset to an old version. Here is what is happening in the world's playerdata folder: Before updating the world, there is one ".dat" file in the playerdata folder(which is the current playerdata of the world). But after updating, a second file appears, which is a ".dat_old" file(which is playerdata from a long time ago when I had different things in my inventory). I have no idea where this old playerdata is even coming form.

How to reproduce:

1. Make a world in 1.15.2
2. put some stuff in your inventory or put on some armour(just change your playerdata a bit)
3. quit the world and join again a couple of times, changing around your inventory each time.
4. load the world up in 1.16
5. there will be a second playerdata file in the playerdata folder of the world, which will be a ".dat_old" file. your inventory will also have reverted to a previous state.