Going through a nether portal causes you to go forward

What is your device model and OS? Are you sure, you weren't tapping the forward button after leaving the nether portal? There is not much information from your video, as it's too short, and we can only speculate, that nether portal is there. Could you please add a longer video with the repro of the bug?

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Now that I look at it, it was probably my controller, and not the game

(yes, I know it says iOS, I use a pro controller with my iPad”

Resolving as Cannot Reproduce based on reporter comment.