Ok, i have a bit of a messed up situation. I'll try to explain this as clear as possible.
I have a 128G SSD with Ubuntu on it. That worked fine, bootet via UEFI and Grub with the bootloader on the same disk.
I now installed Arch on a second 500G SSD. I can't get Arch to boot over UEFI. No clue why, but i never could. So, i set it up with BIOS Grub. This is working perfectly. But after that installation the Ubuntu Grub will only show the grub commandline. I have no clue why, as they are on different disks, which never got touched and one is UEFI, the other BIOS.
I am still able to boot ubuntu manually from grub commandline. Rewriting or Reinstalling Grub through Ubuntu isn't working though.
Since i can boot Ubuntu manually with grub commands, is there an option to manually rewrite the grub with those commands? Any help on that matter would be appreciated.