@Gordyola If the devices are 2.4GHz it may be that they cannot connect to channel 12 and 13, and the "clever" router has decided to select one of those two. Naturally the app and browser interface do not have the detailed features that would help. There may be something in the router logs to indicate why they were dropped or refused re-connection.
If the devices are on other channels in 2.4Ghz or 5GHz it could be that the DHCP timeout needs changing. You have to balance the number of connections it can juggle and how long before they are dropped to make room for a fresh connection. Check your devices for power-saving mode, and not just for the whole device but also for the networking chipset. In Windows it's via Control Panel and then dig deep into the networking devices.
You could have interference. Likely if there's a strong signal at the other side of the property from the router so its selection algorithm is making poor choices.
If 5GHz things are disconnecting try the higher channel ranges (100-144) and (149-177). If it's WiFi 6/6E I'm stuck as I don't have that at home. If you're close to an airport it's just possible that the radar is upsetting your 5GHz WiFi - on that you're really stuck.
If you have an Android device, get a WiFi Analyzer app (I'm sure they exist for iOS too) and wander around looking for dead-spots.
