When a block item is placed inside of an item frame it will render very unusually and not display the whole block.
Linked issues
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Duplicate of MC-45453 - If you have not, please use the search function in the future, to see if your bug has already been submitted. If you could not find the original report, please comment with the keywords you searched for.
And for none block items, I have yet to be able to get them to appear in the frames at all.