I've just submitted v2.3.12 of OPC for the Zen Cart moderators' review; I'll post back here when it's available for download (https://www.zen-cart.com/downloads.php?do=file&id=2095).

This release contains changes associated with these GitHub issues:

#309: Correct PHP notice on missing HTTP_USER_AGENT
#310: Correct PHP notice for missing gender on guest-account creation.
#314: Correct misleading "Shipping options have changed" messaging when cart's changed post-checkout start.