APKs with weak signatures no longer verify, move them to the archive
Don't know if this is a server issue or what is going, but https://f-droid.org/wiki/page/Category:Apps_with_failing_builds lists a lot of failing builds. Looks like the buildserver is going for retrying some quite old builds as well.
To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information