What is your Shotcut version (see Help > About Shotcut)? Is it 32-bit?
22.10.25
Can you repeat the problem? If so, what are the steps?
Adding an MLT file as a clip to the project adds it with an encoded path. The clip plays fine at first (despite the file name looking weird in the timeline), but when you save the project and reload it, the “Missing Files” popup appears for the MLT file.
Probably the fix aready covers this, but just to provide info: also happens on linux, "/"s on the path of opening mlt as a clip get converted to “%2F” escape sequence. Works if one goes to manualy replace them with "/"s in the project file.