The GiveWP Core outgoing plain text Donation Receipt email function is broken when your PDF Receipts add-on is installed -and- activated. Installed and deactivated, no problem.
under review
Ben Meredith
under review
Our team is looking into this, and will have a look.
Issues like this that are not preventing donations or have a simple workaround are generally prioritized at the end of an 8 week development cycle, and then tested and released. That means it can be up to 10 weeks for issues like this to be resolved.