Happened yesterday on Xbox One.

We converted our old world to the Bedrock version, the host started the level and I joined in remotely through my own xbox.

The host was unable to go certain places that I was freely able to. Almost as if his character was simply "larger" than mine despite no visual hint that this was the case.

The host was unable to walk under fence posts that stopped just above his head while I was able to freely walk under them as normal (so the post would have been 3 high).

Similarly, the host was unable to walk through diagonally placed (non-connected) fence posts while I was able to freely do so.

In a few instances the host was unable to lower himself onto a ladder in a 1-cube opening in the floor while I was able to without issue.

In the nether he found it very difficult to navigate through an iron door operated by a switch - again as if his character needed to be overly precise while I was able to just walk to and fro unimpeded.

He was some free black basketball player skin, if that matters while I was some steampunk skin.

Upon saving, quitting, and reloading he was able to navigate these problems without issue. We have not played enough since then to see it re-occur.