By the looks of it, playing the multiplayer at all could cause the game to entirely break; 505 Games advise that all players stay clear of the multiplayer until they release a fix, but the singleplayer and local multiplayer are unaffected.
While we do not know the cause of the issue, it’s likely to be something involved in the multiplayer code.
Terraria released 4 years ago in 2011 for Windows, but has since made its way to all major consoles (including 3DS and Wii U), OS X, Linux, as well as all mobile devices – releasing on Xbox One and PS4 towards the end of 2014.
The last major update Terraria received was version 1.3 this time last year.