I had the same issue, and apparently it got fixed when I sent error reports (from the app) of all the devices that I could no longer connect. I haven’t seen this solution much on the forum, and I’m not entirely sure if it’s working now just because of the sent error reports, but I would reccommend everyone struggling with this problem to give it a go! It’s very easy to do and it’s the only thing that seemed to work for me.
Since this morning, all my LED bulbs were offline and I could not reconnect/reset, it stalls with “Connection timeout” every time. In the last months my devices regularly lost connection somehow, but I always managed to reset them, however this no longer worked now. I tried lots of other stuff first: reset the devices multiple times, change of wifi network, router reset, DNS check, etc. Then I logged in with the dingyichen@yeelink.net account and it turned out all the devices did connect using this account, so I knew the devices weren’t broken and my internet connection wasn’t the problem. I suspected there would be a firmware update available, but this was not the case. I logged back in with my own account, tried to connect my devices once again, many times, but it didn’t work again. Frustrated, I gave up and then decided to send the error reports through the app. To my surprise, 5 mins later 2 of my devices (the ones I sent the error reports from - as an example) suddenly turned online. Looks like sending the error report triggers some kind of troubleshooter from the Yeelight server, and it seems to work!
Devices concerned:
3x Yeelight LED bulb color I
2x Yeelight LED bulb color II
1x Bedside lamp I (had been offline for months)
I’m on the Europe server, and all devices are back online now!