I can't log into my world. I do have the wandering merchant in the area. (Adding this because I saw another similar report but in my case I have a different report)
This is all I got in the log
The game crashed whilst ticking entity
Error: java.lang.NullPointerException: Ticking entity
As you said you have a wandering trader: Duplicate of MC-143404. Please, always include the crash report, and search before posting.