After updating BuddyPress my website won't load or I get a fatal error?

If after updating to BuddyPress 12.1.1 your website won't load or you're getting a fatal error similar to this:

PHP Fatal error:  Uncaught Error: Call to undefined function bp_core_get_user_domain()

It is likely a conflict with bbPress or another BuddyPress compatible plugin. 

Install the BP Classic plugin to fix this issue.