I came across an issue where using a watering can on a crop that was also being accelerated by a growth accelerator was not being affected by the watering can. As you might understand this slows the growth of that specific crop quite a lot.

Is this a consistent issue across multiple minecraft versions?

I first encountered the problem while playing the mod pack All The Mods 3 on 1.12. I have done some more testing and the issue remains while playing on both 1.12 and 1.11.2 with only Mystical Agriculture installed.

This also happens with fertilized dirt or soil from other mods. It just doesn't grow.

I noticed this at version 1.10.2, but i don´t know if it happens because of my created modpack or because it really happens without other, i will try this day, when i will be free

I'll be releasing versions for 1.10/1.11 with this fixed tomorrow. A 1.12 version with a fix will be a bit later.