After losing my connection to the server and logging back in, I did not appear in the player list shown when holding the List Players key (default: tab). Another player that was online could also not see me in the list. I could also not see my skin in F5 mode, the default skin was displayed instead.

However, “Fenhl joined the game” does appear in the server log.

As a workaround, relogging fixed the issue.

Update: This appears to be the result of logging in while the player is still listed as online (which happens e.g. after a “connection reset by peer” disconnect). The player logging back in does not add a second copy to the server list, and when the server catches up and removes the original copy of the player from the server list, the player is missing.