I've analyzed everything I could and there's nothing wrong, neither in your map nor in the script command of the "parallel" event.
The following video shows your map working without any intervention from me:
(The RMMZ and game menus are not in English because I don't know how to do that in this engine, only in RMMV)
I tested it with all available versions of RPG_CORE, from 1.0.0 to 1.3.3 which is the most current.
My advice is, uninstall RMMZ completely.
If purchased at the Delgica store, consult the manual or support for license maintenance.
If using Steam, use the manager.
In both cases, I advise to delete the RMMZ folder completely after uninstallation.
Restart your computer and reinstall RMMZ again, as none of the projects ran files, you won't need to create new ones.
But if so, use the menu to update the test project's CORE, as shown here:
Hello RPG Makers! The latest update, Version 1.3.3 is live! Thank you for using RPG Maker MZ. As always, we appreciate your support! We hope you are enjoying it so far. Download Link Bug Fixes Fixed image errors in tileset. Outside_A1: "Poison Swamp" and "Dead Tree" have a noticeable joint...
I believe that I don't have any other method to be able to help you. So I wish you good luck.
I have no idea why this would be the case, but after loading up the project again, it suddenly works.
And not only that! I realised that the function doesn't actually reset, so you don't need a parallel process, you just set the new focus once and then reset it later. That's awesome!
The only problem is that I don't know how to focus on the player again. Could you help me out one more time, Dev_With_Coffee? Or anyone else?