Target disk mode very slow in one direction

Hi there,

I'm having a problem when using target disk mode and that is has suddenly become very slow in one direction.

I have a 2015 Mac Pro and 2015 Mac Book Pro. Prior to experiencing this issue, I could transfer extremely fast via target disk mode, no matter which of the machines was set the 'target disk mode'.

Tonight I've found that if I set the Mac Book Pro to 'target disk mode' and try copying 170gb, it says it will take approx 11 hours. If I do the reverse and set the Mac Pro into 'target disk mode' then I am able to copy the 170Gb in about 8 minutes which is what I was used to (when in the past I'd set the Mac Book pro to 'target disk mode').

I really need to be able to get the speed back for so that I can use the Mac Book Pro in 'target disk mode' again.

I've tried restarting both machines, tried a different thunderbolt cable, ran disk utility on both disks not finding any errors, tried plugging to different thunderbolt ports, removing other devices...

If anyone has some suggestions that would be much appreciated.

Ross