The wither skeletons in the nether do not move if they are in a wither rose flower or they remain locked and do not jump on top of the rose, they think it is a block and mobs such as piglins, zombies, among others do not move. It doesn't allow mobs to move between roses like in java.
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We're tracking this issue in MCPE-90407, so this ticket is being resolved and linked as a duplicate.
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