Hi there, I’ve been encountering this bug and was able to reproduce a few times.
I’m using 3DS Max 2018, with the latest version of the exporter (20200701.2), exporting to .gltf format.
Basically, I have got a scene with two objects. Each object has a morph target modifier, each using a different target, and the morph weights are animated.
When I create an animation group for the first object, it works and exports fine; but when I create an animation group for the second one in a similar vein, it seems to go through fine, but then re-opening the animation groups window and trying to export the object results in a deserialization error:
It works fine when adding multiple basic animations - such as translation and rotation. The issue seems to be with having multiple animations with animated morph targets.
Worth mentioning that when I click “confirm” to commit the changes for the second object’s animation, I get this weird behaviour where both animations are selected in the left pane - shouldn’t just the animation for the second object be selected? Might be a clue for the cause of the bug: https://imgur.com/a/onvJObf
I am uploading two really basic scenes to reproduce the bug here: one has an animation group set for the first object only and works fine; the second one has an animation group set for each but is in a broken state - attempting to export / open the animation group window will result in the aforementioned error.