At Thrive we update a lot of plugins. A notoriously fickle plugin is the eCommerce plugin, WooCommerce. In a recent seemingly incremental update, the entire shop lost its custom theme templates and were all defaulted to the generic page layout. Did this happen to you? Well, after much searching, the solution was a single line of code missing from the functions.php
add_theme_support( 'woocommerce' );
This is not a new requirement of WooCommerce, but in a recent update its priority has changed. I believe this is the relevant action item in the change-log:
3.3.1 – 2018-02-06
Fix – Protect against theme support being defined too late. Fixes some issues with custom themes defining WooCommerce support incorrectly.
A side note of the same update that was a bit less problematic was a recent change which relocated a few theme options to the WordPress Customize section. There you will now find the options for changing product and category display settings.