I am seeing a frequent error on almost all the pages after upgrade from AEM6.3 to AEM6.5.
core.js:1082 Uncaught Error: Page design could not be loaded at Object.<anonymous> (core.js:1082) at Object.<anonymous> (jquery.js:3411) at fire (jquery.js:3232) at Object.fireWith [as rejectWith] (jquery.js:3362) at done (jquery.js:9842) at XMLHttpRequest.callback (jquery.js:10311)
Is anyone having any information on that, how this can be fixed ?
I strongly suggest you use the 6.3 -> 6.5 migration to move towards Editable Templates and AEM Core Components.
The most likely reason I can think of is that your designs are in a strange place. Please see this article for the changes in repository structure that come with AEM 6.5 and this one for information on how to use the proxy servlet for clientlibs.