I also bumped into similar case. My temporal solution is to move files to a folder which doesn't have any non-ASCII character in the full path.
Full Case Study:
The bug under the following environment had been tested and reproduced.
1. Runing Atom or VSCode with "Markdown Preview Enhanced" plugin under Microsoft Windows 1909
2. Suppose Test.md is the file which contains the following script
Test.md and style.iuml are under the same folder X
3. The full path of folder X contains non-ascii characters, like "工廠".
Error message would be similar to:
[From string (line 2) ]
cannot include style.iuml
If I move Test.md and style.iuml to another folder, for example
Then the problem resolved. What's interesting is even white space is supported in folder path, but non-ASCII ones are just out of scope.