SharePoint 2013 - Office web apps intermittent issue

From past few weeks we are seeing issue while opening the documents from sites error message says “Sorry something went wrong + An unexpected error occur on the Server”.  This happens with individual users accounts(Since it is expected behavior with Service account for Office web Apps). After identifying on which server we are seeing the issue we are performing theIIS reset on that effected Server and then issue will resolve but after a week or 10 days this is repeated again.    If anyone has seen this issue in(SP2013+OWA) please share your inputs for permanent fix.

Subhash