I'm no expert. But I've come to understand that this is a common WiFi problem. A good solid WiFi signal is imperative. You want at least -60 (-50 is better, -70 is worse). And even then, sometimes, for reasons other than signal strength, there can be problems. To eliminate WiFi as the source of the problem, plug in an ethernet cable instead, and see how things go for awhile.
Use the WiFi Strength command on the Maintenance menu. There is plentiful informatation available here in the forum on improving your WiFi quality.