Upgraded to 20w18a and followed the recommended steps here but this issue still persists (on server).
With @Josiah Abram Guthrie on this one, still appears to be an issue with 20w18a. Maps created with an empty map or attempting to regenerate existing broken maps is not fixing them (running server).
Upgraded to 20w18a and followed the recommended steps here but this issue still persists (on server).