Quicktime icon has become Reminders icon?!?

Had the same issue. Context: I had the Reminders.app pinned in the dock and QuickTime.app not pinned.

To fix it I:

• Removed the Reminders.app from the dock (while both apps were closed);
• Started QuickTime.app - and saw that this time it used it's own icon in the dock;
• Added the Reminders back afterwards.
• Done

In case you already had both in the dock, in the first step remove both.

Hope it helps.

Try restarting in Safe Mode (not loading startup items or other software that is not part of a clean install), which will also reset some caches. That latter part is what you’re going for here. Start up your Mac in safe mode - Apple Support. After that, you may start up normally again (not Safe Mode).

Very same thing with me -- I'm running 14.4.1 (23E224) on 2017 iMac Pro

I restarted in Safe Mode, verified through System Information/Software/Boot Mode: Safe.

Restart again in Normal Mode did not resolve this. I am able to keep working; it's just a curiosity at this point. Will try again EOD -- thank you for the suggestion Urquhart1244

I had a similar problem: When I opened Quicktime Player and then pressed command-tab to switch apps, Quicktime Player showed up as Reminders. if I opened reminders and pressed command-tab, it looked like I had two copies of Reminders running.

But removing Reminders from the dock seems to have fixed the problem, so thanks.

This worked perfectly for me (only the Reminders app was docked prior to following steps)