Unhappy [Q] [Help] Debranded M8 does has no LTE/4G

Hey guys,
I hope somebody can help me with that one.

Ago some days I got my HTC One M8 and its O2 Germany branded.
After going through all the procedure of unbranding(unlocking bootloader,s-off,changing CID,international european Stock Rom) I found myself in a situation with a not working LTE connection on my phone. I've tried fixing it with one app called "LTE OnOff" to force using LTE only but it didn't work.

The international european Stock rom for my phone just gave me HSDPA or EDGE/GPRS connection but not LTE.
After trying some Rom's in the hope of fixing that problem I reverted back to my branded O2 Germany Backup.
Only that gave me again a LTE connection.


Does anybody know how I can fix that problem and have LTE on other roms too ? Or is that not possible ?

Thanks guys I hope my english isn't that bad, I didn't used it for quiet some time ..