The same thing happened to me, I started using the software yesterday. (I read the whole post before wrinting here)
I bought the PC version and I'm using the trial on my android.
When working on the PC it kept running without problem, I didnt select any fancy option on the app in android and on the PC, since I work from home, the only thing that I had enabled was the google drive sync. but it was working very well during the morning, it kept running for more than 3h.
I remember that at afternoon, at some point the tracking stopped automatically. I dont remember what time it stopped, but I think it was around 1h40
When I went to sleep I put the software to track my sleep, when I woke in the middle of the night and went to check, it was stopped at 1h40.
I'm feeling that it might have something to do with android putting a process to sleep or something like that.
Now I stopped the sync and I'm going to test on the smartphone and on the pc at the same time for testing, to see if any of them will raise the problem.
As soon as I have a result I'll post again.