Proxypass declining URLs that look the sames as ones it accepts

I'm at my wits end. Why are some working and some not?

Proxypass /public http://localhost:8081/public

Proxypassreverse /public http://localhost:8081

On the debug level error logs:

[Fri Jul 26 13:54:44.331950 2019] [authz_core:debug] [pid 30291] mod_authz_core.c(835): [client 172.20.176.108:7939] AH01628: authorization result: granted (no directives)
[Fri Jul 26 13:54:44.332023 2019] [proxy:debug] [pid 30291] mod_proxy.c(1123): [client 172.20.176.108:7939] AH01143: Running scheme http handler (attempt 0)
[Fri Jul 26 13:54:44.332031 2019] [proxy_ajp:debug] [pid 30291] mod_proxy_ajp.c(722): [client 172.20.176.108:7939] AH00894: declining URL http://localhost:8081/public/repositories/3/archival_objects/3765
[Fri Jul 26 13:54:44.332035 2019] [proxy_fcgi:debug] [pid 30291] mod_proxy_fcgi.c(972): [client 172.20.176.108:7939] AH01076: url: http://localhost:8081/public/repositories/3/archival_objects/3765 proxyname: (null) proxyport: 0
[Fri Jul 26 13:54:44.332039 2019] [proxy_fcgi:debug] [pid 30291] mod_proxy_fcgi.c(975): [client 172.20.176.108:7939] AH01077: declining URL http://localhost:8081/public/repositories/3/archival_objects/3765
[Fri Jul 26 13:54:44.332044 2019] [proxy:debug] [pid 30291] proxy_util.c(2203): AH00942: HTTP: has acquired connection for (localhost)
[Fri Jul 26 13:54:44.332050 2019] [proxy:debug] [pid 30291] proxy_util.c(2256): [client 172.20.176.108:7939] AH00944: connecting http://localhost:8081/public/repositories/3/archival_objects/3765 to localhost:8081
[Fri Jul 26 13:54:44.332056 2019] [proxy:debug] [pid 30291] proxy_util.c(2426): [client 172.20.176.108:7939] AH00947: connected /public/repositories/3/archival_objects/3765 to localhost:8081
[Fri Jul 26 13:54:44.589566 2019] [proxy:debug] [pid 30291] proxy_util.c(2218): AH00943: http: has released connection for (localhost)

I had a similar error message and it was related to security features in PHP-fpm which was only parsing files with certain extensions.

Check out your security settings for mod_proxy_ajp. It could also be the permissions on the socket.

I see, "mod_proxy_fcgi.c(975): [client 172.20.176.108:7939] AH01077: declining URL" so maybe check security.extensions in your config as well.

I was parsing HTML files for PHP which was causing the problem.