After spawning and defeating the end dragon again with the ritual, there is a structure that spawns where the initial portal back to the overworld was but no dragon egg spawns.

This has been fixed in newer versions.

I too am having this issue.
The structures are from YUNG's end island mod and More Dragon eggs mod is what should have added a dragon egg for a respawned dragon. However, it looks like More Dragon eggs is overwritten by YUNG's island mod.

this issue is still relevant in version 0.1.11 and 0.1.12 (both were tested)

Same problem for me. By accident I used my dragon egg on a spawner. I wanted to get a new egg but defeating the dragon a second times does not spawn a new egg. Please fix! Furthermore, the Dragon Egg Essence is also not working (I will open another issue). So I am quite stuck.

Please help :)