Jumping on soul sand with the soul speed enchantment will change the player's FOV, but when you keep on jumping on a block other than soul sand with the soul speed enchantment it seems like it gets extended. This doesn't seem to happen when normally moving away from soul sand, the FOV effect seems to disappear in a matter of seconds.
How to reproduce:
1- Start by obtaining a pair of boots
2- Enchant the boots with soul speed III
3- Place soul sand and start moving while jumping on the soul sand
4- You will notice that the FOV effect gets extended while jumping (this doesn't seem to happen when normally moving away from the soul sand without jumping, the FOV effect disappears immediately)
Observations and Expectations:
Observations: Jumping after stepping on a block other than soul sand extends the FOV effect with the soul speed enchantment.
Expectations: That shouldn't happen since normally moving away from soul sand removes the FOV effect faster than when jumping.
Related to MC-175312
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The resolution of MC-189368 and how similar it is to this issue may be relevant.

Thank you for your report!
After consideration, the issue is being closed as Working as Intended.
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Related to MC-175312