Hi @mark-stanley ,
Yes it does. LoRaWAN is not WiFi where a session is bound to a particular access point, in LoRaWAN the session is bound to the back-end, so once joined every TTN gateway will handle your traffic.
That claim is based on devices sending infrequently at a random frequency and a at random time. So LoRaWAN will not work for 3000 devices all sending on the hour (using a clock). It will work if those devices send at random times within an hour. (Each device can send exactly 1 hour after the last transmission as long as all devices do not send in the same timeslot)
A simple way to avoid this is to have your code generate a random number when first started (make sure to prime the pseudo random generator with something like the current time to avoid all of the node getting the same random number [and do not start all nodes in the same second if you use the current time]) and delay all transmissions on that node that number of seconds.
Best regards,
Jac