It sounds like you have filesystem corruption or permission issues. I would suggest using a live ISO and running sudo fsck.ext4 -p -y -f /dev/partitionNumber. You will need to know which of your partitions is the / (root) partition of Solus, you can check using lsblk. You should keep it unmounted, or at the very least mount to validate it is that partition, unmount it, and try to perform an fsck.ext4.
You can get information on the flags I provided by running fsck.ext4 --help.
If it is a permissions issue, that is a separate matter and would involve you ensuring your user on Solus is the user which owns those files (using chown). If you are using that specific partition with other operating systems, it will affect those as well, and this problem is likely to occur again due to persistent permission issues.
