I'm guessing here since I'm unfamiliar with the itch backend.
It appears that you are missing app manifests as described here https://itch.io/docs/itch/integrating/manifest.html which appears to be related to the itch upload tool, butler, described here https://itch.io/docs/itch/integrating/quickstart.html
This may be a step you just forgot to do, since the previous version of The Fixer worked with the itch app. Or, of course, I could be completely off here.
No big deal, I suppose. Direct downloads will always work.