Pro Tools throws up an Assertion Error if it is unable to find a "Bounce To" location after bouncing in an open session. For example, if the "Bounce To" path is renamed or moved after a bounce, Pro Tools throws up an assertion error, instead of defaulting back to the Bounced Files folder. No other bounces can take place until the session is closed and reopened. Pro Tools then defaults back to the Bounced Files folder. Currently experiencing this in Pro Tools Ultimate 2018.4 on 10.12.6, but the bug has existed since at least PT12, and possibly back to PT11.
DUC thread here: http://duc.avid.com/showthread.php?t=399379