What exactly do you mean with
Do you mean ‘when back to the V2 console’ or have you made any changes to the device settings ‘going forth and back’?
Do you currently have the device defined in both V3 and V2 with same keys? If so the device will estalish a session with V2 because of the V2 gateway (traffic routed from V2 to V3 over packetbroker will be slower so V2 will probably send a join accept sooner).
If so, you will first have to prevent the device joining to V2.
Tips for how to do that can be found here: see part Preventing V2 Joins.