Wifi to Mobile (and viceversa) permanently loses connection


We’re having a problem with our mobile devices (androids on Galaxy A52, A53, & A54. Also tested on Galaxy S21 and Fold Z3)

If ZeroTier is set up while on wifi, everything works great. As soon as they leave wifi to go on cellular, ZeroTier will always have connection problems.

These problems start as a complete lack of connectivity (can’t ping our private data server which is also on ZeroTier) but after about 5 minutes, the pings start working, however any links to the server will be stuck loading at about 5% forever. No timeouts, nothing. Just an infinite load. Going back onto Wifi (that the router ZT is set up on) usually fixes the problem and they will be able to connect.

We’ve tried lower ZT’s MTU, but this didn’t work (only caused issues on the desktop clients - which otherwise have no issues). We’ve also made sure every ZT client (desktop and mobile) are up to date. Tried using an older android build from March, but no luck. We’ve tried enabling/disable IPv6 on the clients, as well as using “RFC4193 (/128 for each device)”. We’ve also used 2 different routers, but nothing has worked.

I’ve found that uninstalling ZT on android (while on cellular), rejoining and authorizing the connection allows them to instantly start connecting and loading pages as expected. As soon as they connect to wifi and switch back off, it will be forever more stuck in the broken state as mentioned above until we uninstall the ZT client and start over.

Our temporary solution is to completely turn off wifi so the phones can never switch connections, and then the ZT client will be fine.

Is this a known bug? Or is there any other type of setting we can use to make it not get stuck in a broken state?

Thank you.

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