Can only comment re/ grind speed: Without bean feeder, 90 RPM was safe for me, 70 RPM stalled only once in >100 attempts, 50 quite occasionally.

With bean feeder and only one chute open, 70 RPM is not causing any issues, cannot comment on lower RPMs yet.

Beans used are definitely light, not moodtrap-light, but SEY/Tim Wendelboe Filter/banibeans etc. Hope that helps!

Just wanted to share my recent experience in troubleshooting and resolving a stalling issue with my Key. Didn't see it come up in the search and figured it may help out someone else next time.

If you remove the back panel and look at the green LED - if if comes online when you turn on the unit and when you press the grind button and nothing happens - check if you see the green LED blink seven (7) times. This means there is a loose connection (the different cables that are running vertically, locked together by a clip in the middle) and you should make sure that each cable is tightly connected.
You may need to pull slightly and then push them together to make sure you hear it click.



Please note that discussion on the second version of the grinder hss been split to Weber Workshops Key MK.II