Comment 12 for bug 1763986

That looks ok. Even if the files are missing, grub customizer can handle that. So I don't know, what's happening there.

Create a backup please and then remove these files step by step and tell which removal was required to fix the problem (with some file content):
- /etc/grub.d/.script_sources.txt
- /etc/grub.d/30_os-prober_proxy
- /etc/grub.d/33_linux_proxy
- /etc/grub.d/21_memtest86+
- /etc/grub.d/proxifiedScripts