Yesterday i updated my system on stable and all was fine. Today there again some packages to update on stable, installing was fine, but after that the kernel modules can't longer loaded on system startup. Error message in systemd: Failed to insert 'nvidia': Exec format error.
After resyncing the mirror list, I see the following error: On all actual mirrors, the coredb can't be accessed and on all other mirrors the local installed packages are newer than those on the mirrors.
Now, I switched to unstable and run pacman again. Now the system is fine again and the kernel modules can be loaded again.
I think, there is something wrong with the stable tree on the mirrors. Seems, that some packages from testing or unstable went into stable, so that kernel and modules no longer suitable? Eventually the testing or unstable tree was synced to the stable tree on the mirrors?