See attached image... I have a scene in which the Horizontal Aperture parm on a camera LOP gets disabled after a certain frame. The logic for disabling the parm is clearly tied to the state of the control parm above, so I'm really confused on this one, as my control parm is not set to None or Block.

What can cause a parm to be disabled on a certain frame like this? No Keyframes anywhere. The camera lop is in edit mode, pointing to an incoming USD camera that is perfectly fine if not affected by this camera lop.

This is in 18.5.462.

It seems that my Camera LOP node may have gotten corrupted somehow. The problem goes away if I replace it with a new one.

What about the expressions on the hidden parms?

If you can post the hip file with the bad camera LOP in it I'm sure there's some reasonable explanation, but you've got me curious... You can probably delete everything in the scene except the camera LOP. Or if you want to explore for yourself, I'd say @jsmack's suggestion is likely the best bet. You can unhide all invisible parameters to see if there are some weird expressions or keyframes that got put in there by accident?

The hidden parms don't drive the visible ones though, it's the other way around, right?

I'll see if I can extract the node, but I should add that it has an expression on it that is reading USD attributes on the camera prim directly, so you'd need the camera too, which may or may not be feasible. I'll see how far I can whittle it down.

Tim Crowson
The hidden parms don't drive the visible ones though, it's the other way around, right?

Yeah, that's correct. I think in 18.5 the camera was changed so the aperture value recorded has the units translated.