The message in the reported warning, indeed, has a wrong syntax, but this is because of the initial part, which was supposed to contain a message type, like UD3
(note that a heading timestamp should have been already consumed before).

The reported exception occurs 4 seconds later, so it may be related with a different line.

You can have the Server log the lines it receives by setting the com.lightstreamer.adapters.remote logger at DEBUG level.
Then, we can check what exactly causes the exception.