When you drink a slow fall potion and then stay near-still with an elytra then you start to rapidly flicker in and out of visibility. This happens when looking at yourself but it does not appear to other players in a multiplayer world (I tested via a LAN world so results might be different if on a server hosted via a different method)
This bug seems to happen whenever you either have very little speed in the Y direction, have next to 0 speed in both the X and Z axis or if you go at very fast speeds.
Also keep in mind that it is quite likely that slow falling might simply make it easier to trigger the bug and not actually be the source of said bug.
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I am able to reproduce this issue in 20w51a.
Can confirm in 21w03a.

This also happened to me on servers in 1.16.X if I was very overclocked with fireworks and turned on the third person front view.
The video is attached.

Can confirm in 1.17.1. Might relate to MC-111516.
Fixed in 24w44a.
I cannot reproduce this. May you share more details?