As the problems seem to have started when you restarted the device, why do think the problem is at the server? Why did you restart in the first place? We’ll need many more details if you want help.
(There is a bug for ABP devices: when editing an ABP device in TTN Console, then TTN resets both the uplink and downlink counters. But you did not make any changes before the problem started, right? Also, see After resetting frame counters, payload is shown on gateway traffic but not in application - #12 by arjanvanb like already mentioned above as well.)