@Electriceye to check drivers to work you cant just use a multimeter, you need to use an oscilloscope to see whether they properly generate steps. Alternately you can use a stepper driver analyzer (search the forum for more info), but in the end that's more or kess an oscilloscope with sone predefined settings.
Blown drivers usually exhibit "craters" or little blow holes, so inspecting them visually is another option. Posting high resolution, focussed photos of drivers here allows us to help determine whether a driver is blown or not.
If a driver looks good, the next most likely culprits are still motor wiring/crimps (testable with a pull test holding the housing and tugging on the wires and solder defects for the pins (also visually detectable).
Regarding the Octopus board: The heatsinks on the plastic housing act much less as a proper heat dissipator than the vias designed into duet boards and the high copper content on the duet board.
The duet boards are best cooled by blowing a bit of air above and below the board along the drivers.
Another drawback of the stepstick format is the inherent current limitation and the usual arrangement making proper cooling on top and bottom of the stepsticks difficult, especially with banks of jumpers blocking airflow.