T-mobile and Three in UK - keeps 'Connection Lost' state or pings

I just moved to UK for three weeks. I bought two sim cards:
T-mobile with 1GB data and Three with unlimited data.

Three works fast on H+ speed but it tends to ping around 16 sec each 2 min which makes it really hard to play...

T-mobile works fast with Youtube, Facebook etc, but doesn't connect to AL at all! It keeps showing 'Connection Lost' all the times which makes it completely unhelpful!

Jeeez... I had no issues with AL in Germany, Poland, Estonia, Russia and now this? What's going on?

Any helpful ideas? Thanks in advance!