Simply put, if the dragon is killed by the mob crusher, the end portal doesn't form and a new dragon respawns shortly after.

Industrial Foregoing Version:
industrial-foregoing-1.16.5-3.2.14.6-14.jar

Titanium Version:
titanium-1.16.5-3.2.8.5-20.jar

*Crashlog If Applicable (Upload to pastebin/gist):
latest.log

Enjoy my terrible marksmanship :D
https://streamable.com/kr7xwi

Initial report. Replicated with only IF and JEI
EnigmaticaModpacks/Enigmatica6#3307

tbh a mob blacklist on that block would be neat, e.g. for the gaia guardian too, there doesn't seem to be a way atm 🤔