Phasmophobia stores your save data locally (in %AppData%\..\LocalLow\Kinetic Games\Phasmophobia ). If a mod launcher miscalculates your XP or item count, it can corrupt this file. You would then need to manually delete your save and lose all legitimate progress.
The vanilla version of Phasmophobia usually runs fine, but players turn to alternative launchers for several reasons: photon launcher phasmophobia download