Suprised to not see this in here, but ever since better together came to fruition you could no longer stack item frames with signs, fence gates, bars back on I belive legacy version item could share the same block if applicable, for example 2 item frames could fit inside the same block
Thank you for your report!
We're tracking this issue in MCPE-14412, so this ticket is being resolved and linked as a duplicate. Specifically other blocks cannot occupy the same space as an item frame in bedrock edition.
That ticket has already been resolved as working as intended, which means this is not considered a bug and won't be fixed. Please do not leave a comment on the linked ticket.
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