Apparently Synching decided to transfer 4.6 GB of who the f*ck knows overnight, even though it’s explicitly set to not do anything when it’s not on WiFi. The phone should have been up-to-date anyway (I did not do anything that would have modified my files), so I don’t understand what data was even being sent.
My cell bill is going to be over double what it normally is because of this, and I am NOT happy.
It’s difficult to say what happened exactly, but I’d say the app can be somewhat flaky, unfortunately .
If you want to make sure this doesn’t happen ever again, you can try to disable background data usage for the app in the Android settings. This will block all background data usage for the app on the OS level.
Alternatively, you could use some type of a firewall app for the same purpose - there are at least several options both for rooted and non-rooted devices.
Actually I was wrong, but also not: The default value from the UI is applied to the config file without any interations with the settings dialog (not even need to open it). However the first time you start syncthing, the incorrect default is applied. I’ll add it to the release scheduled for next Tuesday.
FWIW, I did have the feeling lately that my Syncthing on Android had been running while I wasn’t connected to WiFi. Didn’t investigate further, as there were no consequences on my side. But it would be a big coincidence as well if that moment of surprise were totally unrelated to the recent reports.
I’d have surely noticed the issue myself, but I had to stop using the app altogether a few weeks ago, as I just couldn’t force Samsung not to kill it every few days for no particular reason , so I had to switch to running the bare binary (with root) just to have reliable sync. I still try to keep an eye on what’s going on with the app, of course, but I can’t test new things quickly anymore.
Just in case this is related, my syncthing on my Android phone is set up to sync only when connected to the charger, but a couple of weeks ago I caught syncthing being active while the phone was running on battery. This was confirmed by syncthing on my laptop which showed syncthing on my phone as being ON – that’s how I realised actually. Syncthing on the phone was stuck in that state and only stopped running when I went into settings, I think. I saw this happen only once in the long time I’ve been using syncthing.