Synchronise don't works

For maybe a few weeks, I can't synchronise my account, I've tried to log out / log in multiple times but the "Synchronise now" button does nothing and the "Sync" one on the devices tabs just get stuck on "Synchronising..." but eventually does nothing. I can send a tab to Firefox desktop, but that's all. Both devices are logged on my account. I can't choose what to synchronise because it's greyed out.