My sonoff t1 U.S. with firmware 2.7.1 also disconnect.
Sometimes I open the ewelink app to power on/off the light, but the app shows that sonoff T1 is offline. after about 2 minutes the sonoff reconnects.
The sonoff is about 2 meters of distance of the router.
The solution is what "Stephen Bunting" said. You need to give it a static ip address from your DHCP server in your router. Be careful to make sure to change the range of the other devices as described by "Stephen Bunting" in a previous comment.
static IP is not the solution. No idea why it would be based on the way the communication goes.
anyways, all my SONOFF have a static IP. they work well, suddenly, they disconnect from WIFI connexion (1 meter from the internet box), they will NOT reconnect automatically.
They do NOT appear anymore in my internet box, the blue light is blinking fast 3 times, then 1 time slow, and it repeats that cycle forever..
I have to re-appair, then it works, a few minutes, then it does not work anymore after a few minutes.
it's definitely on 2.4Ghz, no 5 enabled.
THe firmware was 1.6 (!) and being migrated to 3.3, but does not help.
I have only 1 SONOFF that NEVER disconnect (it has 3.0).
i'm wondering about upgrading this one to 3.3 to see if that's firmware issue.
any other ideas?
update: it's not 3 fast blue blinking+1 slow. it's 2 blue fast + 1 slow. in other words each third blinking is slow :-) . That's a SONOFF T1 (switch in the wall)