I also had occasional problems with two Shelly 1PMs; in the end, it was always weak Wi-Fi.
They were always shown in the app, but nevertheless they weren’t updated regularly. And when the data is missing from Venus OS for a while, it causes problems.
even in the immediate vicinity of the repeater, there can be problems. For one thing, your repeater may have a poor connection to its base station; for another, there may be sources of interference, or a shielding obstacle between the repeater and the Shelly.
I’ve already had to change the settings so that the devices don’t connect to the base station that’s furthest away and only just reachable. You can do something about this with the roaming function: simply set the threshold higher so that the Shelly voluntarily switches to the nearer base station!
Different Wi-Fi names can also ensure that the Shelly prefers to use the base station it’s supposed to use. You can enter two connections, after all! It may also help to reposition the Shelly or turn it 180 degrees, which is easily possible with a Plug S.
You can also check the Wi-Fi signal level on the Shelly.
And when I have connection problems, I now always use an MQTT server; it works better than accessing it directly via the web!
As a general rule, you should avoid repeaters, or at least use repeaters that operate in so-called transparent mode, i.e. pass the respective client’s MAC through to the router unchanged. Unfortunately, many repeaters alter the client MAC completely or partially, which can, among other things, cause connectivity problems for network components.
Unfortunately, you haven’t said exactly which devices you’re using.