@Timbo2 

had the same issue after moving from a Huawei B310 to the MR600 (on three also) , kept going to 3G in same location that Huawei had 3-4 bars of 4G, if you forced it to 4G only the signal strenghth showed 0%,  not suprised there's no comment what can they say !!!!

I would suggest this is to do with signal strength,  mast locations, and directions of antennas.
You probably have been through every option, so I won't duplicate. However, I have a single mast connection, and get 100% signal on 4g and 3g and never have an issue with it dropping lower.

At a previous location, anything from rain on leaves to network congestion would see me jumping between distant masts and it was not enjoyable speeds!

@ed696 

Hi,

Just wanted to say that I solved my problem - by switching from Three to EE.

I chose EE because they claimed to have good coverage at my postcode.

That turned out to be true and I now get a reliable high speed connection.

T

@Timbo2 
Can you please let me know what is "EE".

@Kaushal_Pandey Hi Kaushal, EE and THREE is the name of the UK's mobile service provider, like in India we have Airtel, JIO, Vodafone etc.