I am intermittently facing this issue today in my Org . In Chrome I am not able to edit Long Text Area field . Any one aware of this bug/issue ?
It is an issue after summer 15 release. I have also noticed this behaviour and problem is solved after salesforce support assistance.
After clearing browser cache it works fine as salesforce uses cache of browser so that unnecessary loding of view does not take much time for better UX.
As you said it is happening intermittently, check the salesforce browser compatibility with chrome version. If it is also fine please raise case to salesforce for root cause analysis on this.
I hope this information may help you.