Reproduction :
TortoiseSVN 1.14.2 (Windows 11 x64)
A repo with this structure :
- trunk
- - folder (copied from /branches/v1/folder)
- - - file
- branches
- - v1
- - - folder
- - - - file
with branches/v1 merged into trunk in rev 10
right click on the root of the WC of trunk > show log > select rev 10
by now, you only see the folder as added (copy from /branches/v1/folder), not the file
right click on th folder > Export ..., and select a folder
navigate to that folder in the explorer, it is empty.