Apple Home Kit works in bedroom but not living room

I have several Meross smart plugs running devices (mostly lamps) in my living room and my bedroom. Everything worked fine until a week ago or so. Now every device in the living room stopped working, but every device in the bedroom is still working. When I configure and add a Meross smart plug in the bedroom, it gets added to the Home App and works flawlessly in the bedroom. When I take that freshly configured smart plug to the living room and plug it in, it loses connection and says “no response”. When I take it back to the bedroom, it re-connects. The living room devices stopped working after an engineer installed new emlite smart meters, which have an onboard sim-card. The old smart electricity meters did not have an onboard SIM card. It is the only thing I can think of that is different. Is it possible that the meters interfere somehow with the smart meters? WiFi reception in the living room remains fast and unaffected (c600Mbps). The meters are behind a solid wooden door and the devices in the living room are equally distant to the ones in the bedroom. When I leave all the internal doors open, the relative connectivity issues (good in the BR, fail in the LR) remain.