PT freezing every 5 seconds, for 2 seconds

[PPM6]

This is weird. I use PT every day and this is totally new.

Every 5 seconds PT will freeze for 2 seconds. I mean, although it will carry on playing, the cursor line will stop flashing, and sometimes I'll get the beachball, and no buttons or anything will register or work. And if I hover in the menus, they freeze and stop working too. If I click around in those 2 seconds during the freeze, it's like it stores up each action, and does them in quick succession when it comes back.

I have changed NOTHING on my system. I've tried projects on different drives, still the same. All other software runs fine.

I do mostly editing and mixing and currently my system is completely unuseable.

Any ideas?...

I'm running PT 2019.12.0, on a MBP with High Sierra 10.13.6, 16GB RAM, 2.7ghz i7. Focusrite Clarett 8pre USB interface.