Sometimes GC fails to detect Windows

[Radoslav Nenchovski]

At the end of May there was a system update (Arch Linux) after which GC stopped detecting Windows. I ran os-prober in the terminal and it detected Windows just fine but Windows wouldn't appear in the GC's screen to be added as a grub menu entry.
I didn't report this earlier bc I thought it was a local problem only. But a friend of mine told me he had the same problem with GC (the latest version), so clearly it's a bug of some kind.
Then, a few days ago I had to reinstall Arch and Windows did appear in GC's screen. Today I ran GC to check something on GRUB_CMD_DEFAULT and noticed that Windows had disappeared (again) from the entry list. After a few reboots Windows came back to the entry list.
At this point GC is only useable to edit the visual style of grub - font, background, etc. The only way I could keep Windows in the entry list was to add it manually by editing grub.cfg and then make grub.cfg to be read only by using "chattr +i" command on it.

[Daniel Richter (danielrichter2007)]

That's strange. Grub Customizer just runs the system command "grub-mkconfig" (or grub2-mkconfig) to detect operating systems. If you don't change something on Grub Customizers list config, it wont modify something on the detection scripts (/etc/grub.d). Look at this folder. Is there an extra folder named proxifiedScripts? If not, it must be another reason.

Btw.: There's a better way to add extra entries to the boot menu. Put it into /etc/grub.d/40_custom and then run update-grub or use the save button of grub customizer. Then your grub menu stays updatable.