"animate your avatar"

Errm. No, it's not the animations and nor is it to do with Mono. The way these things work, they animate both you and the person you want to hug (the script has to request permissions of both of you, but since you're wearing the object, the permissions are granted silently and automatically).

The gadget then has to move you towards the object of your affections, which it does using the function llMoveToTarget. Because this is a physics function, the way the most commonly used-huggers move you to the person you're trying to hug (and stop you when you get there) got borked a bit when we switched to Havoc 4 (not mono) but Dari Caldwell worked out a how to recode that bit of the routine, and her solution has been in the jira since April last year https://jira.secondlife.com/browse/SVC-1191 and most people have implemented it. If you've having problems with your av bouncing up and down, it's nothing to do with the animation or mono; it's because you've got a very old hug/kiss device.

Or, as Treasure suggests, it could be your AO and the hugger fighting with each other.

I've often been offered taht. But its not really "me" Notice how the girl's leg goes up all coyly? I have NEVER done taht in my life. I much prefer a good old fashioned quick hug with a colple of kisses and a pinch on the bumcheek.
Anyway, by that point the blokes prolly having a cigarette in real.

This.

Be careful, because a lot of the animations out there were written pre-Mono, and Mono handles things a lot different from the old LSL