MikroTik

RB4011iGS+
6.44.5 (long-term)

I logged in via Winbox and could see the CPU was 25% for no apparent reason, however interface & firewall pages did not load any data.    Performed a reboot, and it took 7 minutes for it to fully boot. No Interface link lights until 7 minutes in and it started working, and I could login.  Winbox appeared normal with the exception that it erased all but the built-in interface lists and as such it broke some of the firewall rules that referenced those interface lists.     Anyone else run into anything similar with their RB4011?

Yes see here: viewtopic.php?t=151046

I can also see from a number of 4011's I've got out in the wild that cpu0 get hammered all the time and the other 3 do very very little :/

which is your current firmware in system -->routerboard ??

/system routerboard print

(firmware not routeros)

For me 6.45.3 same as ROS.

Try to netinstall the device to the latest version and see how it goes...