User not found Error on dashboard refresh seen in logs

Hi seeing following error while viewing dashboard in background.

Version Grafana and database
5.2.1 - sqllite

Datasource
prometheus version 2

Steps to reproduce
Leave dashboard refreshing in the background - it is set to automatically refresh every 30 seconds.
This happens for both admin users and viewers.

error
Sep 5 13:39:24 python: grafana t=2018-09-05T13:39:24+0000 lvl=eror msg=“Failed to get user with id” logger=context userId=3 error=“User not found”
Sep 5 13:39:24 python: grafana t=2018-09-05T13:39:24+0000 lvl=eror msg=“Failed to get user with id” logger=context userId=3 error=“User not found”

It then seems to follow with a 401 unauthorized message trying a get on the page that is refreshing.

Anyone got any ideas about this? I have turned on debug error logging but no usefull extra information found. Thanks very much in advance