Little Backstory for those who are interested. If you don't want to read everything skip to the last paragraph.

Many people know that the Platinum Trophy in KHDDDHD hasn't appeared for everyone who was going for it. The problem here lies in the Trophy "Record Keeper" requiring 100% completion in Battle, Story and Items in the Journal. However, for several people the trophy Record Keeper hasn't popped up and therefore the Platinum Trophy was never acquired. Zantetzuken913 and me have been theorizing about this as we were planning on doing Platinum Trophy runs which were endangered of this glitch. He practiced the run on a separate PS4 profile and got the trophy at the end of him practicing the route. I practiced on my main PS4 profile, but on a new savefile so I can do everything from ground-up. I did not get the trophy once I was done. As I wanted the Platinum Trophy nonetheless I tried again on my casual file that wasn't far away from obtaining it anymore and it worked. After completing everything that was required I got the trophy.

We started thinking and came to the conclusion that the reason Record Keeper doesn't appear everytime is because new savefiles were used. The very first savefile on a new account will always be able to obtain the Platinum Trophy. My theory on how exactly it works is that the Record Keeper trophy get's tracked on your first savefile, but not on any other ones. It might be possible to still obtain it if your oldest savefile didn't unlock Star Combatant, Item Collector or Story Teller yet, but that requires more testing as we are not sure about that.

Therefore: If you want the Platinum Trophy on KHDDDHD you will have to play on the first savefile ever created on your PS4 profile. Once you complete every objective you will get the Platinum Trophy everytime. This does not get fixed by deleting your other savefiles and start a new one, it works only on the first ever created savefile. This also probably means that a Critical Mode savefile is not able to unlock the Trophy consistently, but we are not 100% sure about that. We are not sure what exactly causes Record Keeper to glitch so it might be still possible to unlock the trophy on newer savefiles. All we know is that the oldest savefile created on your current profile will definitely be able to unlock the Record Keeper trophy. We currently have 7 out of 7 examples of savefiles/profiles where the Platinum Trophy got unlocked this way so we are pretty confident in this theory.