https://www.reddit.com/r/PokemonBDSP/comments/re5w3x/music_bug_against_giratina_in_ramanas_park/?share_id=tyk75_bw_IpH-WUPSGemL&utm_content=2&utm_medium=android_app&utm_name=androidcss&utm_source=share&utm_term=1
Funny thing is, I actually got the idea from this thread. The OP specifically mentioned they saved, and I remembered that for all 3000+ of my encounters, I was saved in front of the giratina.
This does raise some questions about does it matter where you save, like in the room, outside of it, etc. I do remember accidentally moving before encountering it, so it definitely has to do with save position.
Thanks again for your help though!