@t3p3tony I mounted the board virticaly with standoffs of about 5 mm onto a piece of multiplex wood and its not built into an enclosure so around 5 cm around the PCB are cable mount trays. The electronics of the printer are at the backside, not enclosed from air. So it gets ambiant room temperature as cooling. No fan is mounted.
I have also another printer with duet wifi and duex 5 running, also same mounting mechanism and even running 1200mA on all steppers. I have been running that printer without ever receiving this warning for over 1 year now with almost daily use.
I know the drives are cooled through pcb copper, but the copper surface area at drive 5 is severly smaller because of the hole for a standoff. That made me think its not getting proper cooling.
I can try swapping 5 and 6 to see if that changes it from 5 to 6 (with setting back to 1000mA) but my printer is now 100% occupied for the next couple of days.
For now I also added small 4988 heatsinks to the ICs of drive 5 and 6 and running 800mA for around 6 hours now, maybe I will leave it like this.