Mission 6 boss glitch?

[Neo-Abobo]

I've encountered a glitch at the mission 6 boss that has prevented me from progressing. Im wondering if anyone else has had this happen and if so, how they worked around it. What happens is when the bosses HP bar is around 10%, the boss glitches out and vanishes, just flat out disappears. The HP bar remains and the music continues, but im stuck with no way to finish off the level. Ive replayed the level about 10 times already, tried different difficulties, different weapons to try to finish off the boss, but the result is always the same. I have also tried deleting the game and reinstalling it. I'm using the physical disc from red art games, if that matters.