Hello Bram79,
Thank you for using Apple Support Communities. I see that you're receiving an error message after recently migrating content to your new MacBook Air. You've come to the right place! I'm happy to help.
First, I recommend using the following resource to download the latest macOS Combo Update:
Download macOS Mojave 10.14.6 Combo Update
If the issue persists test in safe mode. Starting in safe mode allows your Mac to run certain checks, remove caches, and prevent login items from automatically launching. This can isolate possible third party issues. Use the steps and information in the link below for assistance with safe mode:
Use safe mode to isolate issues with your Mac
Let us know the results. Please include additional error messages and any other troubleshooting steps you may have tried.
Have a nice day!