Setting animation blend times in animations imported from a .blend file

Godot Version

Godot 4.2.1

Question

I have some animations I import directly from a .blend file. I inherit a scene from this .blend file, and this scene has an Animation Player.
Initially, I was able to set the blend times for the imported animations in the Animation Player (through the “Edit Transitions” option). However, after modifying the .blend file a few times and saving it (which reimports the file), the option to “Edit Transitions” became greyed out and now I’m not able to set blend times anymore.
I’m confused as to why it happened, when initially I was able to do it. Furthermore, the blend times I did set before it was greyed out are still active.
How can I recover the ability to set blend times in these imported animations?