How to fix the «Error filtering template: Unable to unserialize value» Magento 2.2 failure of a CMS widget rendering?

dmitrii_fediuk (Dmitrii Fediuk) September 30, 2018, 8:39pm 4

Another solution: How to fix the «Unable to unserialize value» failure while upgrading Magento from 2.1.x to 2.2.x?