I don't have any images for this yet since it's random. But on the random chance that I fail looking in grendel's lair or taking a closer looks at the sleeping dreki and I'm supposed to battle them. I can't I go to move off the tile to prompt the battle button to come up but they just dissappear.

I also have never been able to do this one specific event encounter. All my wolves (for explore) are maxed in everything except maternal and charsmia like how do you get a coin from this. (See image)

Not sure about this because its my first time participating in the event but got some pictures of what you are talking about

Yes and no I 9/10 times get the coins for the Dreki and Grendel. But on the off occasion I need to battle him I can't they just disappear.