That doesn't explain why one Firestick is fine and the other is flakey.I think as your only real problem is when in Norfolk, sorry if I’ve got this wrong, I think your best solution would be a waterproof box with m1 in and stick it on a long pole.
We stop in Suffolk during winter and with Poynting antenna still only get very low speed but good enough to stream using a Firestick with some buffering on some channels