Are those OTAA keys? Or are you using ABP (in which case the node does not really “join” the network, but has already joined be generating the ABP keys in TTN Console).
- For ABP: ABP node stopped working → Fixed by creating new ABP… Why?
- For ABP, if you have been sending a lot: ABP / How much Framecount deviation is allowed?
And do the gateway logs still show the packet?