PKI issue: OCSP failing

I have a Server 2016 install, with OCSP and ADCS installed. I have been fighting with OCSP for about two months now, and cannot get it to show green in Enterprise PKI; the ocsp directory itself is empty. I have tried everything in every forum I have found, including:

-Following the instructions in the "Windows Server 2008 PKI" book (we actually bought this book just because of this issue)
-Setting the AIA to http://internalname/ocsp
-DNS entry for the above works fine for http://internalname/CertEnroll
-Made sure NETWORK SERVICE is "full control" on OCSP template, and inside Responder configuration
-Added the CA's computer account in cert template per instructions
-Revoked the CA Exchange cert and re-generated
-Set the ca\UseDefinedCACertInRequest 1
-Tried the -vocsproot delete / -vocsproot
-Checkboxed "Include in the online certificate status protocol (OCSP) extension" in the CA properties > Extensions
-Tried box unchecked an checked "Include in the AIA extension of issued certificates": checkboxing this gives me another red X in Enterprise PKI of AIA Location "Unable to Download"
-Added "Everyone" to read permissions of "C:\Windows\systemdata\ocsp" itself in the File Explorer security tab

IIS logs themselves show the requests are getting to the web server:
2018-11-07 19:08:25 10.15.40.80 GET /ocsp/MFQwUjBQME4wTDAJBgUrDgMCGgUABBRGUB/CXSUFffn3OV
/WbxXSOCA2AQUzjFqwNeWNr0xIWMdJnEOWW0HBAwCEyMAAALd3BlDUOS5l48AAAAAAt0= - 80 - 10.15.40.131 Microsoft-CryptoAPI/10.0 - 404 2 64 0
2018-11-07 19:08:25 10.15.40.80 POST /ocsp - 80 - 10.15.40.131 Microsoft-CryptoAPI/10.0 - 404 2 1260 62

I exported a newly-made cert, and did a -verify -urlfetch on it, and I see:

---------------- Certificate OCSP ----------------
Failed "OCSP" Time: 0
Error retrieving URL: Not found (404). 0x80190194 (-2145844844 HTTP_E_STATUS_NOT_FOUND)

The directory at "C:\Windows\systemdata\ocsp" is empty. The Online Responder config shows "Working" and green checkboxed. I looked through the Security Event log and saw no related errors, although I'm not exactly sure what event IDs I'm looking for.