I'm thinking you have the same problem I do https://community.cambiumnetworks.com/t5/ePMP-2000-and-1000/PPPoE-Problem-has-me-at-my-wits-end/m-p/88578#M13802
From your description it looks like maybe you do not use separate management IPs for your radios so when one of your radios is unable to get a PPPoE connection for whatever reason the radio uses the factory default 192.168.0.2 address. Once the radio gets an IP from the PPPoE server that becomes the address you access the radio with ?
We found that sometimes deregistering the customer radio from the AP causes it to authenticate.
If you find a solution to this please let me know, we have been struggling with this problem for months now. If you have an outage that causes the customer radios to not be able to access the PPPoE server for more than a few minutes you find that ALL of your ePMP radios will not get a PPPoE connection when it comes back up. After much screaming and panicking (it's really fun when over 700 ePMP radios do this at once) we finally figured out that rebooting the access points (effectively deregistering ALL the radios at once) causes "most" of the ePMP radios to get a PPPoE connection when the AP comes back up and they reconnect.
Really though, if you figure this one out let me know.