There currently exists an ongoing issue between TML and vanilla in Steam, in which Steam Cloud data would get randomly corrupted in memory, resulting in crashes and/or broken entries seen at player/world screens. It has existed for quite a long time, but became much more apparent since recently.
The issue can currently be avoided by either starting Steam in offline mode, or by manually moving data off of vanilla's cloud at the page linked below, and avoiding putting Worlds & Players onto the Steam Cloud in the meantime, both in vanilla and TML.
Link: Sign In (Requires logging into Steam.)