Hi! I had this same issue happen to me early July and we couldn't really troubleshoot to find the reason behind it.
I have a suspicion on a couple of things that might be causing it, though.
1) Did you take part on the PSN tag change earlier this year? We know that the leaderboards were hosted on the game's website back then, which means that any unforeseen changes to your tag would not be reflected and therefore not tracked anymore. This would only apply if you ever played the game before the issue happened.
2) The game hasn't been updated, at least not for a decade, so no sneaky code has been implemented to the servers that might change anything. However my PS3 is on the same Software version as everyone else's, and clearing the cache & game data did nothing too.
I used multiple alts during the July incident and found that all of the accounts hosted on my PS3 had this same problem; after performing the stat copy glitch (which is a bit harder to do if your account has this bug) no match progress was saved, while my partners got all of their respective xp.
I can also confirm that the issue is not necessarily related to the regional game version that you own, as my same exact American copy worked perfectly fine in 2011/2012 (you can check my trophy feed for it, used every veil ability back then) but suddenly in 2019 my progress would simply not save.
tbh it just sounds like we got screwed by an unstable progress tracking system. Wouldn't be the first time progress had been wiped for random accounts on this mp, and it certainly didn't get a fix then. As a side note, though, does anyone have another PS3 they can try to do this with? Since my previous console was a Slim (as opposed to a Super Slim now) that might have some value on the troubleshooting end. It's a longshot but I'm also not gonna boost 20 hours straight for 3 trophies, no offense.