I can confirm that errors you reported us are due to a connection interruption between the Lightstreamer server and your remote Metadata Adapter.
Maybe the implementation of notifyUser method in the custom code of your Metatadata Adapter got some errors: it seems that instead of replying to the server your adapter closes the connection in the case of user validation request.

Given the periodic recurrence, the issue could be caused by a burst of requests that always occurs regularly at the same time.
What do you do within the notifyUser method? Maybe some request to DB or other external services that can saturate and get stuck in case of overload?

Regards,
Giuseppe