Bug has existed since the release of 1.15.
Basically, bees will try to path-find thru glass panes and iron bars, causing them to be stuck infinitely because they'll never move. If you hold a flower, they will path find towards the player, but afterwards will then pollinate flowers/crops, and then get stuck trying to go thru glass. This issue is not existent on solid blocks, as in my farm, they only try to go through the panes.
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We're tracking this issue in MC-206304, so this ticket is being resolved and linked as a duplicate.
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Duplicates MC-206304