Taking everything we have said into account, I would reflash the BTU UK firmware and activate additional options in Odin3 (I have done this several times to “flatten” the system. This has never caused any damage).
In Odin3 v3.13.1 open …
Options
set a tick (activate) in each case for
Auto Reboot
Nand Erase
Re-Partition
F-Reset Time
Pit
DREAMLTE_EUR_OPEN.pit
included in file CSC