Constant signal drop on RP2!!!! Please help!!!

Hi
I am with Vodafone in UK. Just bought my RP2 and unfortunately and annoyingly I have a problem that seems very common with RP2.
The phone is on regular settings 4g/3g/2g(auto mode) LTE activated, all on...
After a while and on a constant basis the newtork just stops working and when it manages to come back it's only going on 3g despite the fact that I'm in Central London and there's no reception shortage.
I've already tried a few "tricks", the internet doesn't seem to be short of that ,unfortunately without permanent results.
Can anyone here help me please.
Thank you.