Developer question; but open to anyone with a theory..

[Isaac]

Does anyone have an idea of what might cause an animated [custom*] model to vanish in plain view, for rotating the camera... As in, it's right in front of the party, but tilt the view a few degrees and it's completely invisible. I've had this happen on a custom lever and button models.

*Obviously this is the key point... When it's custom there could be anything wrong with it... but I'm hoping someone has had this exact symptom, and knows the general reason for it.

[petri]

Objects are culled by their bounding boxes. Bounding boxes are computed from the unanimated models. Make sure that the modeling pose resembles the animated object. E.g. don't lift buttons off the ground with animation -- do it in the model.

[Leki]

For monsters, you have to keep capsule node in viewport as well, if I am not wrong, and there is still a "lot of alchemy" during exporting multi meshes modelss (like monster + weapons), so you have to "play with propper linking". For big single meshes like dragons you can try to make big box, let me say 15x15x15m (5 cells) and texture that "moster body part" with one alpha blended pixel (=make it invisible), but there is still "capsule in viewport issue", if I remember it correctly.

In other word, try to describe, what you want to achieve or share model here.

[Isaac]

Brilliant answers both; I'll see what happens; but I bet it works.

**Update: This did seem to fix it completely! Thank you both very much for the insight. It was good that the setting is alterable in John's GMT utility, and that I did not have to re-edit and export from Blender, then reposition everything.