With the setup, Sprint has been set to Toggled, and the sprint key was unbound (It also happens when it's set to Hold, and when it's bound), and there shouldn't be a way to stop sprinting
Hitting the other player while being attacked has a chance to un-sprint, with the particle still there, hitting any entity again will start the sprint again (except it doesn't happen on the server side - no particles were shown to other players), and being hit again will stop the sprint.
It happens on a lot of servers, so I think it's safe to assume it's a client-side issue.
- duplicates
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MC-69459 Client-server desync when player attacks while holding sprint key
- Reopened