(1) I thought this was noted previously, and discussed.
I know I’ve run into some weirdness with section planes animating between scenes myself.
EDIT: This is the previous topic:
(2) I was always under the impression that Pages#show_frame_at(t) method was for inspection purposes and not really for heavy custom animation. At least I myself have never and would never use it when writing an animation plugin.
There are too many other strange things that happen (or do not happen) if we try to use the rudimentary built-in scene animation feature, (ie, some properties like hidden and materials not interpolating but just switching 100% on the 1st frame, and the strange interpolations of target to eye paths [ie, the distance is not static as one would expect.])
Myself, I’d always use an abstract Sketchup::Animation class.
Yes, it’s more work, but you have so much more control.