Hello.
I ran into a probably quite rare conversion problem: A Soft Hyphen, when inserted before a word (ie between a space character and the first character of a word), can cause the space character not to be converted (epub > docx).
Naturally, I am aware that such placement is very strange for Soft Hyphen. I don't know how such Soft Hyphens could get into epub. In any case, I have seen several documents exported in this way, and it is very difficult to fix them without access to the source epub file…
sample epub+docx attached
Calibre version: 6.26