The post has been updated since in exploring it further, the upgrade and the occurrence of the issue (links redirecting to the home page) appears to be coincidental.
Instead it points to add_filter( 'rewrite_rules_array', 'disable_embeds_rewrites' ); which has been added to the functions.php file.
The steps to reproduce these are;
1. Embed the code `add_filter( ‘rewrite_rules_array’, ‘disable_embeds_rewrites’ ); to the functions.php file.
2. Access Settings > Permalink
Digging into WordPress further, the action results in the internal WordPress rewrite rules being replaced with an empty value.
To resolve the issue, either remove and/or comment out add_filter( 'rewrite_rules_array', 'disable_embeds_rewrites' ); when upgrading WordPress and/or accessing the permalink settings. The problem may also manifest if a plugin interfaces with permalinks (untested).