When the player dies for any reason in the nether when they re-spawn in the overworld they temporarily become a "ghost player" (ghost player meaning they cannot interact with entities and blocks). This also happens when you leave the end through the end portal going back to the overworld. If you re-log after returning to spawn in either case, the player is not saved at their spawn, but instead put back where they were before the action that caused their return to spawn (i.e. death or end portal). This has affected 1.13-pre4 through the current version.