We are aware that people use the export feature numerous times. If in the mean time a font file is in use by another process, the font export will fail as it can’t overwrite a locked file.
When you save a file from a web browser, it will append (1) to the file name to overcome this problem. E.g.
I export my fonts to a folder that is not tracked by MainType and copy them from there to a folder that is before installing them. I then delete the temporary versions after making a backup of the exported fonts.
After fixing any bugs in the new fonts, I uninstall them and repeat the process.