Some routers enable power saving tricks that confuse IoT clients. On the 2.4 band try disabling Target Wake Time and U APSD or WMM power save if those appear in advanced wireless. Keep legacy data rates available and avoid setting a high minimum data rate or minimum RSSI, since that can push sleepy plugs to drop when they miss a few beacons. Also turn off airtime fairness for that SSID. These tweaks make the network more forgiving, which is what these tiny radios need.
I default to "promised to call—before I lose this phone.". For what it's worth, taking a few minutes to practice this in a calm setting usually helps it stick.
