Sonoff zigbee dongle going off line temporarily

I have 4 Sonoff zigbee dongles around my home, 1 is obviously the main one connected to my main box via usb2 cable and the other 3 are in router mode around my home.
Recently, a week ago, I started to get disconnect warnings and the dashboard items related to plugs/contacts went “unavailable “ for a minute or so before it all comes back on line again. It’s driving me crazy, I’ve removed some redundant sockets and moved and reset stuff but still the same.
One of the items is the gate contact and therefore I get earrings via Alexa throughout the day telling it’s open then closed again as it goes through it cycle.
What I get reported in the individual Sonoff routers is “became unavailable” and then “turned on”

Hi, welcome to the forum!

You could first check this if there is anything in there: Zigbee network optimization: a how-to guide for avoiding radio frequency interference + adding Zigbee Router devices (repeaters/extenders) to get a stable Zigbee network mesh with best possible range and coverage by fully utilizing Zigbee mesh networking

Which Zigbee integration are you using?