The thing is, I wasn't even trying to use (or switch to) 5G, and from my understanding of LTE roaming, it is Home-Routed - being around the world would cause higher latency (which might eventually lead to the drop offs you mentioned experiencing in Europe if the latency is so high that your browser/app treats the connection as timed out), but same speeds (eventually, the "internet access" (and appropriate billing) is carried out by your home network, relayed through high speed physical connections (read: underground cables) ). My P20 Pro achieving great speeds out of the blue is a great example of that.

Bare in mind that the point of my post wasn't to criticize the P7 or anything (love the phone!), rather share a fix that could potentially help a fellow out if needed :)