I have the same problem re: gardening with butlers. I told the butler to stop gardening and he didn't listen and kept gardening so I thought perhaps the instruction wouldn't take until after he finished.
I later went to tell the butler to start gardening again (I had finished the first tier of the gardening aspiration) and the option was still to 'stop gardening' even though I had told him to stop before. Also, I noticed the garden was drying out so I ended up assigning the task of 'water plants' in order to get him to water the plants.
I also notice that time won't go in ultra speed if you have a butler awake on your lot, though I notice the same with any NPCs on your lot (or if you are trying to nap in a public area). I think the slow speed in public areas is recent, and particularly noticeable in San Myshuno as I've done a lot of rags to riches and I don't remember time not going to ultra speed when the Sims were napping on benches in the past.
I have no mods or CC and play on a Windows 10 gaming laptop.
Thanks!
Jennifer