Slow initial app window opening, but only in certain situations?

I use some apps that can accept files a few ways:

1. open and then use its own file select dialog
2. "open with" from Finder
3. "drag & drop" from Finder

Method 1 is fine and the app responds as expected.

Methods 2 & 3 result in the app opening—you can see the app's menu bar and dock icon—but then there is a delay of 4 or 5 seconds before the app window appears.

Apple say:

Engineering has determined that your bug report (39378510) is a duplicate of 19293778 and will be closed.

But why the delay? What is macOS doing? How can I remove the delay?

I've tried:

• reset launch services (no difference)
• new/guest user account (no delay!)

Most interestingly:

1. Build new app with unique ID (no delay on first launch; delay on second launch)
2. Delete Saved Application State for the app (no delay!) but this regenerates with every run of the app
3. Deleting only the file data.data (download that file) in the Saved Application State (no delay!)

Workaround: I can prevent Saved Application State on a per-app basis. See here: https://github.com/sveinbjornt/Platypus/issues/110#issuecomment-377398429

Any ideas appreciated.

• mac OS 10.13.6
• no antivirus

Here are two videos:

• xACT.app: https://youtu.be/IzUbQaPzAhA

• Platypus.app: https://youtu.be/Omn0pHl7oQw

So it seems that the app is for an as yet unknown reason tied-up opening its com.organisation.AppName.savedState from ~/Library/Saved Application State/. I found this out by using FSMonitor whilst launching the app and confirmed it using AppCleaner.

Looking inside the .savedState file I can see that there's a file restorecount.plist, present for exactly as long as the delay, which contains an incremented number which on my install of macOS is about 544,000,000 right now. Half a billion windows restored since Mac OS X 10.7 Lion! The ID seems to be system level, as even the Guest user has roughly the same number in its savedState files.

I'm still interested to know why a new account has faster generation of the restorecount.plist file whilst "old" accounts can be a lot slower.

The workaround is to either:

1. per-user: enable System Preferences > General > Close windows when quiting an app
2. per-app: in Terminal defaults write com.organisation.AppName NSQuitAlwaysKeepsWindows -bool false which stores it in the app's preference file at ~/Library/Preferences/.

Further discussion at this GitHub issue.