My first zigbee device was Sylvania (73685) rgbw led strip. On it's own it worked fine but once I started trying to add sengled zigbee bulbs I kept having problems with pairing the bulbs or keeping them connected. Zigbee uses 2.4ghz so I thought maybe interference so lowered power output on wifi AP 2.4ghz band & even turned it off for testing but didn't help. I think I read somewhere that sylvanias caused that problem. I unplugged sylvania led strip, reset & rejoined everything else and had zero problems. Tried to add the sylvania back in and disconnect problems came back after awhile. It was past the return period so now I keep it unjoined and plugged into a zigbee smart outlet. I sometimes have to remove power from it to join new devices or when I restart zigbee controller. Currently have mix of sengled bulbs, thirdreality plugs, sonoff plugs & sensors, and single aqara tvoc all working together fairly reliably.
Aqara devices can be finicky with non-Aqara devices, especially router devices.
I've personally also had much better results with Aqara devices since switching to Zigbee2MQTT and a Sonoff Zigbee stick, I had a lot more dropouts with ZHA and a Conbee II stick.
I have your exact setup. Have you done any tweaking? What channel are you on? All I can think is, I have thick concrete walls. Changing battery also didn’t help.
I haven't done any channel optimisation so far, I probably should do. I have the P version of the Sonoff Zigbee dongle, I haven't tried the E version.
I've also been careful with picking router devices. I've tried to avoid router devices that have poor reported compatibility with Aqara. There is a page/thread somewhere online where people were compiling lists of devices that do or don't play nice with Aqara. IKEA devices apparently work very well with Aqara, I've been using their smart plugs wherever I can.
My Zigbee network also improved a lot when I set up some IKEA plugs in the loft. My house also has thick walls, but it seems Zigbee signal can propagate more easily through ceilings/floors.
Using quality brand batteries also seems to help a bit, at least from a battery life point of view.