This module is designed to fix a simple problem. Apparently after migrating data from Magento 1.x to Magento 2.1, this error is encountered. I believe this is due to a problem with how the attribute sets are copied.
The solution is inspired from:
This is super simple:
composer require swiftotter/advanced-pricing-bug
php bin/magento module:enable SwiftOtter_AdvancedPricingBug
php bin/magento setup:upgrade
php bin/magento setup:di:compile
php bin/magento setup:static-content:deploy
php bin/magento cache:clean
php bin/magento cache:flush
php bin/magento indexer:reindex
add this line in your .ini file
max_input_vars=10000
or put this in your index.php file
ini_set("max_input_vars",10000);