My list only contains ~30% of the devices on my network.

If so, where do you find the list of all the hosts connected to your network?

Thanks!

Maybe just after switching over to another router?
You have to wait until everyone has renewed their lease...

Yes, we did change routers. I guess I thought the release would have happened by now.

Thanks.

Depends on what your lease timers are set for, if the device is on and passing traffic and/or if it is communicating with the DHCP server. 

No it does not depend on traffic passing.
It depends on the lease time set in the previous router.
When that was set to 1 year, it can take half a year before everyone has re-requested DHCP

You can look in IP->ARP to see which devices are active and compare that with the DHCP lease list.
When there really are a lot of clients there, I would recommend visiting one such a client and look what
is happening.  Check the DHCP client state and see how long the lease is valid.

No it does not depend on traffic passing.
It depends on the lease time set in the previous router.
When that was set to 1 year, it can take half a year before everyone has re-requested DHCP

Actually it does. If the host is sending DHCP requests packets but the DHCP server never sees them thus the host device never receives and offer. The host will assign itself an APIPA address. 

No it does not depend on traffic passing.
It depends on the lease time set in the previous router.
When that was set to 1 year, it can take half a year before everyone has re-requested DHCP

Actually it does. If the host is sending DHCP requests packets but the DHCP server never sees them thus the host device never receives and offer. The host will assign itself an APIPA address. 

Apples and oranges. If a client has a 6 day lease from a previous DCHP server, it's not going to bother requesting a renewal until 3 days have passed from the time it got its lease.

Your situation is one where a client sends a DHCP discover packet but receives no response. OP clearly stated that he just switched his router (DHCP server).

To answer the 'how long' question: the average client will take 50% of the max period, so if the old lease time was 1 week, then you'd expect about half of your hosts to renew within 3.5 days. You will have 100% updated after 7 days from the time you shut down the previous router.

A quick and dirty way to force the issue is to reboot your access switches, causing most clients to renew their leases when they see their link drop for a few moments.

Thank you Zero, I will try that out.