Ok - found an issue.

I've tried setting "manual fan speed"
and played around with the maximus auto fan control - but some of my cards just dont want to run the fan speed i set in 1Bash.

When i was running off 1PSU with 8 cards it ran perfectly.

I just added a second PSU to my ASROCK BTC PRO board to run 13 cards and 4/ 13 of the cards wont adjust their fan speed correctly.

EDIT: With every restart its getting less and less stable - fan speeds are NOT changing on majority of cards now.