Multiple Essentials Lock Ups with Feature Services

Hi,

Has anyone had the experience of Essentials sites becoming very unstable when feature services are added?

Our main site here has been running well for a while then after some testing (where there were no problems on data) I added a point, line and polygon feature layers from one service to allow drawing of symbolised fire behaviour.  

But ever since it was added we're getting very bad performance and the site is locking up at least once a day.  Log files just have repeated severe errors "Operation Completed Successfully"... (not much of an error message!!)

Remove the layers and we go back to stable performance.   The feature service is hosted a local network AGS from SQL Server 2008R2 data.  No security.  Some definition queries on layers limiting the data collection date to last week.

No workflows involed, just using the edit toolbar.  90% of our users wouldn't have even touched the feature service since was in a theme.

Thanks,

Peter