After upgrading from a pre-TSM version of Tableau Server (2018.1 or earlier) to TSM (2018.2 or later) on two or more nodes in a cluster, you are unable to access the Extensions feature in Tableau Server Settings > Extensions due to the error:
An unexpected error occurred while processing your request. Try again. undefined
Attempting to save changes on this page results in the error:
Some or all of the settings failed to save. Try again.