(Local) Self-hosted could be the reason for problems with existing and new reservations at specific properties.

After some system program code update, wouldn't it make sense to repopulate the reservations (database vs program code) ?

Rather new to Hyatt, but in general when something (eg. reservation) disappears or doesn't appear to begin with, initial thought is the "system" doesn't know and so the property might not have your new reservation and existing reservation might not receive credit for nights/points.