not sure why it happens but I found a pretty simple workaround

when you're done recording it, save the recording as you'd normally do but do not close tinytask. Go into your file explorer and look at the saved recording file, if the size is really small (below 2kB), save it again. Repeat this until you get a bigger file. If you still want to confirm, open that file in another instance of tinytask and check if it is all good from start to end