LH tracker orientation randomly offset 180 or 90 and unfixable for lighthouse / positional trackers

[stephen304]

Background info

SlimeVR v18.1.0 (though I've had this issue with 0.17.0 too so it's not new)
Vive 3.0
Tundras
Cheesecake slimes

I use slimeVR with a mix of slimes, tundras, and vives

This sometimes looks like:

• Vive chest/waist, slime thigh/leg
• Vive chest, slime waist, vive thighs, tundra feet

In slimevr settings, I manually only enable the waist tracker, and every time I am reassigning all the trackers to ensure nothing is swapped. I have reset all slime settings several times and it doesn't impact the bug.

The reason I do this, mainly the second combination, is because LH occlusion on the waist is terrible with how I sit. But using LH works fine for my legs and reduces the amount of drift I have to deal with. Meanwhile, slimes work fine on my hip, but I can't use them on my thighs because they lose connection as soon as they go horizontal (I sit down).

The Issue

It seems that when SlimeVR 'adopts' a LH tracker (my chest vive in this case), the mapping of the tracker's orientation to what is used internally by Slime seems to randomly be inverted 180 degrees, and weirdly sometimes even 90 degrees. So my vive is pointing forwards since it's on my chest and shows up properly in steam overlay accurate to the real-world position, but the movement of slime's IK waist tracker moves in the inverted direction compared to what it's supposed to do based on the chest tracker. In the chest tracker's details screen, it appears that the z vector is pointing towards where my chest would be instead of away, whereas the other trackers have the z axis pointing out the 'top'.

Symptoms

Whenever this bug happens, even after I've done a full reset / mounting / yaw reset, tilting my chest forwards causes the virtual waist tracker to move forwards instead of backwards. Likewise, leaning / laying back which would normally position the virtual tracker in front of you actually causes the tracker to move behind the chest, as if you were laying forwards instead.

Since it's completely 180, it also means that leaning left causes the tracker to go right, and vice versa.

Weirdly, it seems like only the derived position of the waist tracker is inverted, the rotation of the waist tracker derived from the bugged chest tracker seems like it might be correct. It could be that the IK is using the inverted rotation of the chest tracker to derive the position of the waist tracker in IK, but the rotation of the waist tracker might be calculated correctly using non-inverted orientation of the chest tracker. I haven't looked at the code much so I don't know if this is plausible.

This gets even weirder when it's 90 degrees offset, as leaving forwards/back causes the tracker to swing side to side and vice versa.

Videos

Example of the 180 degree inversion:

Recording.2025-12-13.123824.mp4

Example of the 90 degree offset

Recording.2025-12-13.124731.mp4

The only way I've been able to work around the issue so far is to keep restarting slime and steamvr until it works properly, it seems completely random whether it works, and trying to invert the mounting with manual mounting doesn't seem to do anything.

Aside from this bug, using slimevr with a mixture of slimes and LH trackers works fairly well, so it would be amazing if this could be smoothed out.