I find that the decay time is very jumpy in the lower settings. It’s hard to get small decay amount. Only a tiny movement creates a jump in day time. Please see the video: https://www.youtube.com/watch?v=My6_1p0cfG8
Is this the case for others as well?
Mine behaves in a similar way, but I don’t consider this a malfunction
One thing that might be confusing is that past 12 o’clock there doesn’t seem to be any change, at least when you have an arpeggiator running. The thing here is, there is no way to set the gate length on the Grandmother’s arpeggiator (whereas you can on the Matriarch) If the gate length is shorter than the decay time, then the decay knob won’t make any change after certain treshold
If you use a software or any external arpeggiator or sequencer where you can set the length of each note, you might be able to play with the Decay knob with it’s full range
Thanks for your reply bichuelo - sorry that I’m so late to the party 
Unfortunately even sending very short gate times with the DAW to the GM doesn’t change the behaviour. I really wonder why this could be the default behaviour. For me this is just faulty. I’ll contact Moof support.
I got response from Moog: this behaviour is intended - The pots used to control the envelope are logarithmic pots and will therefore have an exponential response as you move the pot through its full range.
Okay, I guess a matter of taste - at least my baby seems to be healthy 
Glad to know!
Can confirm is normal GM behaviour.
You can get very divers ARP EG profiles playing around with VCA MODE setting, as well as patching -ENV > VCA AMT IN (will invert the EG profile).