According my result of looking for the reason the shelly 2.5 seems to be designed "close to the edge".
There are reported differences in temperature in case no, one or two of it´s relays are swiched on (even without load). In addition there seems to be a difference in case the power measurement is used/activated (tasmota). Some also report that the temperature behaviour is different if you use it in rollershutter mode or relay mode(shelly software).
And in case of asking "the shelly people" they just say that it is designed for roller shutter -> no big loads.
So I have several of these devices in use. Some for my rollershutter and some in relay mode for lights but all of them are ok and no temperature problems but they are installed behind light switches/in the walls (expecting environmental temperatures of ~25°C).
But the "problematic" 2pcs. shelly 2.5 are used for 3-way motor operated valves (max. load 10W) and are not operated often. But based on my control logic I push 1 relay continously in on-state to be sure and protected against water. So one relay is/should be switched on 24h/7d of the shelly but of course the MOV is not in operation(is in end position) so no load. In case I disable this (all relays are off) temp is ~84°C.
Biggest reason out of my view for overtemperature is the installation environment which is a junction box together with a Shelly 1PM for a 1kW pump. This shelly 1PM is below 48°C so this clearly shows the design difference between single and double relay type of shelly.
To be honest I cannot realy understand the specification of the Shelly 2.5 which says 10A each relay and max. 40°C environmental temp. This does not fit to my experience and to many others. In case you like to have a look there has been one tasmota temp issue (other reason) but you can have a look to the thermal pictures which clearly shows the design "close to the edge"
https://github.com/arendst/Tasmota/issues/7991
https://bleepcoder.com/de/tasmota/58666 ... ce-8-2-0-1
Therefore I do not really see a chance to get happy with the shelly devices and thought of replacing these. First I thought of removing the plastic housing of the shelly or drill some wholes for better ventilation in it but after those thermal pictures, do not believe this will work for long term usage.
Because of limited space in the junction box I cannot use a relay board or sth similar, also because I need the inputs for detecting the end position of the MOVs.