I was happy to learn about Todoist and became a Premium customer in a matter of hours, as this was just the tool I needed. I've now been using Todoist for about a month I would say, but again and again I've experienced synchronization issues, and this has really become a nuisance.
I'm using Todoist Web on Chrome on 2 different PC's, of which one of the PC's have 2 installations of Windows. So I have 3 Windows installations (Windows 8.1) where I use Todoist Web from. I've used the Create Program Shortcut in Chrome on all Windows installations, so I have a shortcut to Todoist.
And then I'm also using Todoist on my iPhone.
What I'm seeing, is that sometimes a task is listed twice on my iPhone. However, I've learned to just ignore that, even though it annoys me.
But I'm also seeing situations where one or more of the Windows PC's are not in sync. Usually it's the deadline information on tasks that are not in sync. I've seen it with parent tasks where I initially set a deadline, create child tasks with deadlines, and then later removed the deadline on the parent task.
But I've also seen it on normal tasks, where I've removed the deadline or changed it, and this is just not propagated to some of the other clients.
Usually I can fix the sync issue on the Windows PC's by either emptying my browser cache or logging out and logging back in. But some days later, the problem comes back again.
I'm sorry to say this, but it has come to to the point that I'm starting to lose faith in my system, which is devasting to the central point of GTD: Having a system you trust where you can record the things you need to do.
I really like Todoist for the simple user interface and the features, so I really want to keep using it. But if these sync issues are not fixed, I will not be resubscribing when my subscription ends.
I can see on this support forum that I'm not the only one experiencing these sync issues, so I would really encourage you to make it a priority, to fix these issues.