Magento 2 "Whoops, our bad" on every product page

Try re-indexing using the Magento 2 CLI

ssh into the server where your Magento files are and go into your Magento root folder.

cd /var/www/html/magento2

From that folder you can access the magento 2 cli with

bin/magento

If you can't start it, use chmod +x bin/magento

in order to re-index data via the CLI, use the following command

bin/magento indexer:reindex

If you want to be sure that NO cache is kept, you can remove the following folders from the var directory with:

rm -rf var/cache var/generation var/pagecache var/di

and then re-compile magento using command

bin/magento setup:di:compile

I hope this will help you.