I also had this problem about 3 weeks ago. Maybe an update was to blame. What I did and what also worked: I set the settings under "Motion detection settings" on each camera (I have three) to "wrong" values, back up to the start, stopped and restarted the app and corrected the settings again. Since then my cameras have been recording again. I suspect that the settings that were displayed in the app did not correspond to reality. By changing and resetting them, they were probably synchronised with the app again.
Now it works again, but I have to say, the software and its quality is stupid China crap. They are very cheap, that has to be said. But quality has its price and you certainly don't buy that here (purely software technically, the hard is ok).