Actually snapdragon is the one with poor gps signal, even on new high end phone u can lost signal. So read review before buying any phone, xiaomi is worst i know.

Google is best friend, search something for the model like "mi 9 gps signal lost + forum". U can find many complaints on xiaomi phone gps but very few complain on oppo etc. People in Android section not really heavy tester, many of them will say xiaomi gps have no problem for example.