[RPi5] WiFi Problem

Devices need to use passwords when connecting and/or reauthenticating to the network. This happens in normal use. It happens a lot more frequently when signal/connectivity is poor; and RPi boards generally have poor(er) connectivity before we place them into cases that reduce it further. So the short answer is "nobody knows" (could be any and all of the items you've listed) but if the issues reduce when moving boxes closer to the router, it's probably the normal issues seen with RPi boards, and the solution(s) are moving things closer, using an external wifi dongle with better connectivity, using ethernet instead of wifi, etc. etc.