Retract GIMP_2_99_4 from downloads. (Work can NOT be exported due to exporter's bug).
In the #6142 (closed) issue (plugin crash exporting as PNG, JPEG, TIFF, and FLI) lists 39 similar reports.
There is no sense in bugging (pun intended) beta testers as no other bug can be reliably discovered in a preview/beta release that does not allow one to complete his or her work.
Keeping GIMP_2_99_4 Windows that is not at all useable for two long months only discourages wannabe testers from participating next time.
git-describe: GIMP_2_99_4
Build: org.gimp.GIMP_official rev 1 for windows
[...]
plug-in 'file-png.exe' aborted before sending its procedure return values
plug-in 'file-jpeg.exe' aborted before sending its procedure return values