3A Nue switches disconnecting

Have multiple 3A Nue switches, 1 gang, 2 gang and 3 gang and was most happy with them, supplied DTH worked fine but last week they suddenly started disconnecting from the hub, now down to 1 that still works, this is in the same room as the hub but then another in the same room disconnects. I can reset the switches and then they reconnect and work but as soon as I move to another room to control devices there they stop again. At the same time other devices on zigbee, Z wave and Wi-Fi/app controlled still work in the hub. Very confused as to what changed. Checked the DTH at the 3A site and no updates. Anyone have any ideas?

Should have also added that the switches still operate by manual pressing just no app connectivity

Some more data on investigating this and talking to the supplier. The 1 and 2 gang 3A Nue Switches are able to added and work using the standard device handler supplied by the supplier. However, after about 4 minutes they become unresponsive and loss communication to the app. However, they stay online in the IDE continue to process manual switching on the switches as well as handle automations, even where they are receiving a prompt from a local device like like a motion sensor. They however will not respond to to the app. If you reset them, they appear again in the app for about 4 mins then are again unreachable by the app. The supplier claims this is an overload of the hub and I should install a second hub in my home?? I did test this overload theory by killing the home in the hub and IDE. The connecting the hub, 3 Aeotec plug adaptors to act as repeaters and then a single 1 gang 3A Nue switch. Same problem. I also connected the switch to my Hue network and again the same thing happened. Appeared then went none responsive. I have 28 devices in my hub including 8 child switches. The supplier insists that the switches are not the problem and has had me moving the hub, recommended range extenders which are not a thing for Zigbee and finally the second hub which is recommended against by many. Any suggestions out there, is the supplier simply ducking or is this a known type of issue?