Magento 2 customer-data.js:90:23 [object Object]

I have literally wasted a few days trying to debug this issue and finally got a definite solution or work around I would call it. Hopefully it can save a few other people the headache I currently have!

I first noticed this error appears when I switch from Client-Side to Server-Side Compilation in Stores->Configuration->Advanced->Developer->Frontend Development Workflow

Then I determined that customer-data.js uses the localStorage within the browser itself to store a variety of information, so you can clear the Magento Cache all you want and you will still have issues.

TLDR:

The fix in Google Chrome is hit F12 to open the Developer Toolbar, then select the Application tab. Clear the Local Storage, Session Storage, and Cookies. Reload the page and all should be well. You will have to do this on your admin page as well.

Credit: https://github.com/magento/magento2/issues/6410#issuecomment-243704461