No Disk Error but Volume can not be Mounted
I have 2 disk RAID 1 Volume showing 0 ERRORS on both Disks but still can not be mounted.
See Report attached please
Your internal disk is failing and has caused at least one kernel panic.
The volume problem is the directory was somewhat damaged and macOS attempted to auto repair, but it failed and let the disk marked as unmountable.
Your choices are:
restore from backup
Disk Drill to recover the data, copying it off to another drive
Disk Warrior to rebuild the directory. (best option)