I have an instance of unboundtest running with Unbound 1.19 here:
https://unbound19test.fly.dev/
This might be helpful for debugging, especially while unboundtest.com is on 1.18.
I won't guarantee it sticks around forever.
Thank you @mcpherrinm and all the @lestaff for going the extra miles in supporting us! 
And one running 1.18: https://unbound18test.fly.dev
https://unboundtest.com/ now has 1.19 as well, thanks @jsha!