We have the ticket and our Web team are investigating why the asset is getting stuck. I had already bugged this one myself a couple of days ago and we do also have analytics/warnings for these fails, so we don't really need the extra bug reports, but thanks if you do send one. Similarly, the footer link to the bug reporting page being broken is bugged already and is being fixed soon.
However, I just wanted to comment on the "make a local package and upload that instead" comment. That is not a suitable workaround and you would/should only get a message that the asset package is not suitable (that it's missing its manifest). A local package is specifically for use outside the Marketplace and is intended for passing packages between team members, but could also be used for linking to in tutorials, selling on other sites/services, e.g. You can optionally codesign the local package to mark it as yours, but this still would not make it suitable for uploading to our Marketplace.
Also, sorry for the misinformation, but Mark's advice there is incorrect. It's not the .yyp project file you upload via the website; it's the .yymp file the IDE created for you when you tried Update Existing Package on the Marketplace menu and it failed. You try to upload normally and if it fails during the upload you can retrieve the package from the location which is written out in your compiler log and then use the website to upload that same file. This is primarily for users with unreliable internet or firewall issues with GMS2 itself, but everyone has the ability to do this on their Marketplace panel. It can be more reliable if the asset is larger than 20MB and so you're getting the "entity request too large error" - in this case, use the website to upload that .yymp file.