Listen, yesterday I was digging into MIJ Developer (app) and ran into one of those post-update headaches that makes you question your sanity for about forty minutes.
So here’s the situation.
I had MIJ Developer installed and working fine. It’s basically a lightweight dev utility — project scaffolding, quick builds, some local server helpers. Nothing exotic. Then I updated macOS. Standard system update, nothing dramatic. After that, MIJ Developer refused to launch.
Not a crash with a report. Not a spinning beachball. Just… nothing. Click, Dock bounce, gone.
At first I thought it was the usual Gatekeeper thing. But there was no “can’t be opened” warning. No “damaged” message. Just silent exit.
What I did first (and why it didn’t help)
Naturally, I deleted the app and reinstalled it. Fresh download, moved into /Applications. Same behavior.
Then I assumed maybe some cached config was conflicting with the new macOS version. So I removed:
~/Library/Application Support/MIJDeveloper
~/Library/Preferences/com.mijdeveloper.plist
Related cache folders
Rebooted. Tried again.
Still instant exit.
At that point I opened Console and filtered by the app name during launch. That’s when I saw the clue: “Library validation failed” and references to hardened runtime.
That’s when it clicked.
What I realized
macOS updates sometimes tighten security policies around code signing and library validation. If an app bundles dynamic libraries or plugins that don’t meet current signing requirements, the system can block them from loading — and if the app doesn’t handle that gracefully, it just terminates.
Apple’s overview of Gatekeeper and runtime protections is here:
https://support.apple.com/en-us/102445
And the developer documentation explaining notarization and hardened runtime requirements is here:
https://developer.apple.com/documentation/security/notarizing_macos_software_before_distribution
Even if MIJ Developer worked perfectly before the update, the new OS version may enforce stricter validation rules.
So it wasn’t that the app suddenly broke. It was that the OS changed the rules.
What actually helped
Instead of reinstalling again, I tried launching it once more, then immediately went to:
System Settings → Privacy & Security.
Scrolled down, and there it was: a message saying MIJ Developer was blocked because the system couldn’t verify it.
There was an “Open Anyway” button.
Clicked it. Confirmed in the dialog.
Launched again.
This time it opened normally.
But I didn’t stop there. Because the Console log still showed some warnings about library validation.
So I checked whether the app still had a quarantine attribute:
xattr -l /Applications/MIJ\ Developer.app
Sure enough, com.apple.quarantine was present.
Removed it:
xattr -dr com.apple.quarantine /Applications/MIJ\ Developer.app
After that, launches were consistent. No more silent termination.
While I was double-checking that I wasn’t missing something obvious, I found this page useful — the resource I used:
https://uggbootsshop.com/developer/31914-mij-developer.html
It reassured me that others were seeing similar behavior after macOS updates.
Why reinstalling didn’t fix it
This is the part that trips people up.
Reinstalling the app doesn’t reset macOS trust decisions. And it doesn’t automatically clear quarantine attributes if the file was downloaded from the internet again.
Also, privacy and security decisions are stored at the system level, not inside the app bundle. So deleting the app doesn’t necessarily clear those policies.
If the issue is code signature trust or notarization enforcement, reinstalling the same binary changes nothing.
Why the update triggered it
Apple steadily increases enforcement around:
Hardened runtime
Notarization requirements
Library validation
Runtime code injection
An app compiled under older SDK assumptions might still work — until an OS update tightens validation.
If MIJ Developer bundles helper libraries or plugins that aren’t signed properly, macOS may refuse to load them. And depending on how the app handles that failure, you get a silent exit instead of a friendly message.
If it were distributed through the Mac App Store, the signing and notarization would already meet Apple’s current policies. You can always browse alternatives via:
https://apps.apple.com/
But standalone developer utilities sometimes lag behind on notarization updates.
After the fix
Once I explicitly allowed it in Privacy & Security and removed the quarantine flag, MIJ Developer behaved completely normally. Builds worked. Local services started fine. No crashes, no instability.
Which confirmed the core logic wasn’t broken. It was purely a policy issue.
What I’ll do differently next time
If an app stops launching immediately after a macOS update, I won’t assume compatibility bugs first.
I’ll:
Check Console for code signing or library validation errors.
Look in Privacy & Security for a blocked app notice.
Check and remove quarantine attributes if needed.
Reinstalling will be step two, not step one.
Quick checklist for future me
Launch once to trigger any security block.
Open System Settings → Privacy & Security and look for “Open Anyway.”
Inspect Console for signature or runtime validation errors.
Remove quarantine attribute if present.
Avoid disabling Gatekeeper system-wide unless absolutely necessary.
It’s kind of funny — macOS security is doing exactly what it’s supposed to do. It’s just not always great at explaining itself.
Anyway, if MIJ Developer suddenly refuses to open after a system update, don’t panic. It’s probably not broken. It just needs a little nudge in Privacy & Security to remind macOS that you trust it.