Read Only flag set on boot

I'm having a bit of an issue - I have an external drive that will always mount as RO when my mac is rebooted. When I do a diskutil info on the volume it shows - Volume Read-Only:          Yes (read-only mount flag set) How do I reset the read-only flag so it can be written to and it remembers that setting when reboot. I'm running 15.1.1. The only posts I can find at the moment are about either re-formatting the drive, not an option currently, or NTFS related issues and my drive is APFS. Thanks in advance..