Placing a sign across an item frame with an item will prevent a comparator output from the frame . Destroying the sign allows detection after the frame has been updated (item rotated).
If the frame is opposit of a banner the frame will give no RS output after it's been updated. if the banner is removed it can give an output after it's been updated.
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Thank you for your report!
However, this issue is a Duplicate of MC-45619.
It has been linked to this report. Please search before reporting, as it's likely that one exists already.
This behavior actually isn't new to 1.13, and (at least according to that ticket) affects all non-air blocks. My guess is it's an optimization to avoid looking for entities when not needed.
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