Comment # 21 on bug 1046500 from Wolfgang Bauer

Well, I tried deleting and adding panel quite a few times meanwhile (including
the "Default openSUSE panel"), and nothing unusual happens here.

But, I am using ext4, so if it is related to btrfs it's clear that I can't
reproduce it.

TBH, I somehow think that you are actually affected by bug#1017461 now (though
it would be strange that the problem occurs when adding a panel, but that may
be coincidence).

Try to disable quotas and see if it helps.
snapper set-config QGROUP= NUMBER_LIMIT=10 NUMBER_LIMIT_IMPORTANT=10

And/or try to uninstall btrfsmaintenance temporarily (and reboot) to disable
the automatic btrfs balance stuff.