You answered yourself?

Afaik the default location for BT receivements is according to /home/user/.config/user-dirs.dirs.
And if it goes to MyDocs, 1 GB could be too less. You should have seen a warning like 'you are running out of space'.
Please clean up MyDocs a bit and try again.


Or if user-dirs.dirs point to /home/user, then you may have run out of space on /home partition or even harder to see out of inodes.