Certain characters in file names can glitch file transfer
One of my files has a % in its name. When I drag the file and drop it in Jami's window to send it through Jami, it will show as being 0 B, the % will have been changed to a %25, and sending it does nothing. If however I click the paper clip icon to manually pick the file rather than dragging and dropping it, it will show as 3 kB and transfer just fine. I think there may be other invalid characters besides the percentage symbol, but I haven't tested.
Test file attached for your convenience: teste___teste.mqres
Edit: turns out GitLab also doesn't like the % symbol (which was between both "teste" words) and eliminates it, so you'll have to create your own test file.