ESET Internet Security blocks access to web configuration of CPE210 (includes solution)
Putting this here in case anyone else runs into this, might save you a few minutes of head scratching.
I finally updated the firmware on my CPE210 from what it came with (1.3.3, I think) to the latest 2.1.0.
It rebooted and was working, but I could no longer enter the setup page from my either of my Windows PCs. Worked fine from Android and iOS and Mac devices!
On Windows, regardless of which web browser, I got a blank web page. Doing "view page source" revealed what looked like sensible HTML but with random binary garbage at the end.
To cut a long story short, I run ESET antivirus, and it seems to be blocking the content of the access point's web page. To fix it I just added the AP's IP address as an exclusion in the web protocol filtering.