Same for me, i am in overall ranking always at around rank 850-900 even if i went to sleep and got 0 additional photos. When i check my rank up its correct, while my period ranking is 1450ish and when i look that one up its wrong and i find myself among the 850s
Now i have no clue if i am within the top 1000 or not.

period 1853, event 1375. Havn't had time to aim for the top 1000 this one :P seems like the lower your rank, the bigger the gap between the 2

Nutaku has changed something in PeroPero Shop, maybe it reset ranking.

The problem with the rankings appears to be fixed now.