Debian Sid updated Grub today and when os-prober ran via update-grub it did not detect my OpenSuse Tumbleweed partition. The update had installed the new Grub so I could not boot into Tumbleweed. Now I have held all the grub packages so I won't be faced with this again. The Tumbleweed grub installation and it's version of os-prober does detect both Debian and Fedora on another partition. FYI Fedoras os-prober also doesn't detect Tumbleweed but that's a problem I'll report to them.
Hi Frank, This is most likely a grub issue - the defaults have changed to *not* run os-prober by default. If so, edit /etc/default/grub and set GRUB_DISABLE_OS_PROBER=false then run update-grub this will fix your problem. Or run dpkg-reconfigure on your grub package (either grub-pc or grub-efi-amd64) and the latest grub packages will ask you about os-prober.