Could you attach your working HDT dll + xml files (or if there are more suff in new builds)? That way I could examine if it's only version related.
Here is the plug-in I have:
I think this was the version right before the version when the plug-in was split into separate files to control certain settings. It should contain the .dll and the hdtPhysicsExtensionsDefaultBBP.xml (which includes the belly nodes--but since you have XPMSE, you should be fine). You can replace the hdtPhysicsExtensionsDefaultBBP.xml with your own if you don't like the settings for it.
Any chance you can make a version of the khajiit / argonian tails that replaces the vanilla ones and still uses the existing animation + HDT? Also, right now it seems those tails "neutral" position is too high and should be closer to vertical. They should also probably be a good bit heavier. The tails also come out of the butt too high, much higher than vanilla. It would also be awesome if there was collision between tails / bodies / walls, etc. (especially with bodies for all those animations which don't animate tails)
Great start though.
Thanks. I cannot promise those additional changes, but if you or any other modder wants to make it and share, I give my permission to utilize the resources and do so.
I am aware the tails are not perfect and are totally reliant on the settings I currently have, but I tried to do what I could. The tails could be loosened a bit more to dangle, but for me the jittery glitches tend to happen more often when I make it that way. If I set the range of values is too high or too low, the physics freak out. The same happens when I turn on the collision properties. There are just too many variables bouncing around that the more that is implemented, the higher the chances of the physics freaking out (for me though, not sure about others).
I do acknowledge that the tails (at least for female khajiit and argonians) are a little high up mainly because it was positioned with a CBBE-style body for reference and not the vanilla model. Also, aesthetically, I prefer the base of the tail to be starting at the spine's sacrum than to protrude out from between the two butt cheeks. You can change the positioning of the tail if you like in NifSkope by either moving the mesh and Apply the transform and save; or by simply moving the 'POS TailSpine','POS TailSpine1', and 'Tail Main' bone nodes to the placement you desire and save (Translation Z-axis if you want to move the tail up or down, default is 0, and remember to do it for both _0 and _1 weight).
Hope this helps and thanks again!