Yep I thought this was odd but doesnt effect playability
I did have a strange issue on my vita 2000 yesterday, where loading a save game would leave all enemies invisible. If I then died and respawned they would be visible again.
I copied the save from my vita to my PSTV to test but could not reproduce it. I then re-copied all files (full version of wolf3d) other than the save file (SAVEGAM0.WL6) from my PC back to my vita and it was resolved.
Unsure if there is a config file I overwrote or if somehow one of the data files became corrupt (although enemies were visible again in the same level after I died...), strange. Was hoping that it would also occur on my PSTV so I could provide the save file to aid reproducing the issue.