When the player has the slow falling effect and engages the elytra, and then proceeds to rapidly move the cursor in one direction to make the player spin, it prevents any forward movement and even in some instances makes the player descend even slower, rather than just continuing to move forward. While this is happening the player and elytra model may glitch and disappear and reappear while in this state. It is possible to return to normal by shifting the cursor enough upwards or downwards, and then the player with the engaged elytra will proceed to move normally again. There was nothing unusual in my game's logs after performing the glitch several times.
In the attached video I do it twice, with the first demonstration's descending speed barely even noticeable, while with the second demonstration the player descends at the normal slow falling rate, but exhibits the glitch with the player model. In both instances the player cannot move forward, only downwards until the cursor is moved enough.
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Looking at MC-187456 and I can see that this would be a duplicate of that bug, but I can't see how what I'm describing and MC-187456, are a duplicate of MC-127949. I do know that you get to glide longer normally when you have slow falling, which is intended as MC-127949 was marked as. But what MC-187456 and I talk about is the entire halting of forward motion with slow falling even when you are facing forward, which appears like it shouldn't be intended, given how normally with slow falling you can still move forward when you aren't directly facing upwards or downwards.
MC-187456 was resolved as a duplicate of MC-127949 , so this is a duplicate of MC-127949