How a file looks in a list through explorer is a function of the program associated with it and is individual to our own computer setups.
Maybe we should concentrate instead on the two worlds between which travel is being attempted. If either or both are overpopulated or overly complicated, that can overload the travel transition even with all of the protective mods in place. Can you travel one sim, as a test, between the two worlds succesfully? Or no sims at all? (double-click on them in the travel dialog to send them all over to the left side in order to transition between the two worlds without any sims "on board")
Does attempting travel only on a freshly started up game session help? How about if you temporarily reduce all of the graphics related Game Options to the bare minimum before doing the save and reload before travel -- the game will not look nice that way, but it's just temporary to see if we can get the transition to complete with as little stress on it as possible.