My friend and I have had the same problem with Fortnite for a few weeks now. Whether in creative or normal public, we stop sprinting for a fraction of a second every few seconds. Sometimes we run against invisible objects, but if you go there again, there's nothing. On YouTube, many say that the solution is to "sprint by default," but I've been on seasons for a few seasons, and if I turn it off and on, I still have this bug. For other YouTubers or streamers, I see nothing like that. I ask for advice.
Is just Fortnite…
I would recommend you to uninstall this game as I do not like it.
'(Sarcasm) Please do not take it seriously!
Now to the own answer:
Do you play on PC, PS4, XBox
Did you write to Epic GamesSupport?
I had the bug too. Reinstall his Fortnite easy, worked with me again.
PC with controller. And no, I have not written Epic yet
Now. I deleted it and reinstalled it. Does not work. The bug is still there
Sorry then.
It worked for me.
Then please contact Epic Support.