/Users/myaccount/Desktop/untitled folder 8/my.app: bundle format is ambiguous (could be app or framework)
In subcomponent: /Users/myaccount/Desktop/untitled folder 8/my.app/Contents/Frameworks/Sparkle.framework
(1)
That sounds like the copy of Sparkle is signed with a different identity. Is this a straight enhanced applet? Try copying the script into a new document and saving.
The goalposts for code-signing have moved a bit with notarizing – signing without notarizing is now pointless for anyone running 10.4 and later.
I’ll look into getting SD Notary working in 10.13. It does a deeper signing that eliminates this sort of problem.