At this time, item frames will simply pop off when the contraption they're attached to starts moving. It would be nice if they could be moved along, as they are a nice decorational utility. (They could potentially also be used in an elevator for floor selection purposes.)

I understand that they are entities, and thus would likely require a decent amount of special casing, but I figured I'd still post this suggestion. Thank you!

Will anyone of the devs reply?

I guess there's now Placards in Create that are a block entity rather than a regular entity, and that obviously moves together with the contraption as intended. As far as elevator selection goes, that's also resolved by the elevator pulleys and contraption controls.

Technically still a bug as the item frame should count as attached to a contraption like a torch should, but it sounds non-trivial to fix, and maybe not worth the effort in comparison to what else the development time could be spent on.