Huh I used a modified version of the latest TWRP from a member that allowed the system to be mounted read only as squashfs is a read only file system ie. The system image has to be rebuilt to make changes. I assumed that since supersu is now system less it those not require system access but maybe it those but I really didn't see the use of mounting it read only as it cannot make any changes to system. Will edit thread thanks for info.
Thanks, I will try your TWRP and report back.
Your TWRP made all the difference: