Do you have 1 or 2 gateways? If you only have the RAK, then what does the following mean?
And what about the gateway(s)’ Traffic page(s) in TTN Console, do you see the packet there? (Note that this page only shows live traffic, no historical traffic.)
What is the device’s last frame counter (or the current one, if you can grab a packet from the gateway’s log and paste that into an online decoder). And is the frame counter configured for 16 or 32 bits?
If the device is using ABP then due to a bug simply changing anything in TTN Console will already reset the counters.
Did you also restart before starting to investigate? Did you restart while the HTTP Integration was having problems? Is it using OTAA or ABP? When it’s using ABP you’d also need to reset the counters in TTN.
(And no, there’s no maximum age for an application.)