On a LAN server, it will connect me for a few seconds then automatically disconnects me and gives me this message: Internal Exception: io.netty.handler.codec.DecoderException:com.google.gson.JsonSyntaxException:com.google.gson.stream.MalformedJsonException: UseJsonReader.setLenient(true) to accept malformed JSON at line 1 column 1
Thank you for your report.
However, your ticket has been resolved as a duplicate.
This issue has been linked to the original bugreport: MC-82968. You can find or add further information on that report.
Please search before reporting any bugs, as it's likely that one exists already.