RewriteEngine rules ignored by Apache on SSL

I have a working Apache setup on CentOS 7.6 using the standard Apache 2.4.6-88 package, using HTTP. I am trying to enable HTTPS on the server, and everything works, except for my RewriteEngine rules. I cannot find any mention anywhere about RewriteEngine not being supported for mod_ssl.

I enabled HTTPS by installing the mod_ssl package, and Apache is now serving both HTTP and HTTPS from the same setup. There is a VirtualHost declaration in /etc/httpd/conf.d/ssl.conf, I haven't touched that. The relevant part of my configuration looks like this:

# Set up Apache proxying
ProxyRequests Off
ProxyPreserveHost Off

# URLs to handle locally
# Apache built-ins
ProxyPass /icons !
ProxyPassReverse /icons !

# Handle local URLs through Apache
RewriteEngine On
RewriteRule ^/$ /index.cgi [L]
RewriteRule ^/favicon.ico /ssg/favicon.cgi [L,R]

ProxyPass /ssg !
ProxyPassReverse /ssg !
ProxyPass /index.cgi !
ProxyPassReverse /index.cgi !
ProxyPass /robots.txt !
ProxyPassReverse /robots.txt !

# Hand off everything else to the Varnish backend, which will in turn
# forward to the appropriate backend server process.
ProxyPass / http://localhost:6081/ retry=0
ProxyPassReverse / http://localhost:6081/

The proxying parts work, all URLs except for the ones listed with the "ProxyPass !" rules are handed off to the Varnish back-end.

The Rewrite part only works for HTTP, however. So http://myip/ will redirect to http://myip/index.cgi and http://myip/favicon.ico to http://myip/ssg/favicon.cgi. On HTTPS, it does not work, and is instead proxied to the Varnish backend (which promptly reports an error).

I must be missing something obvious here, but I can't for my life figure out what.

Enabling very verbose logs, it seems to just completely ignore the RewriteRule parts:

[Fri Dec 14 13:38:30.248204 2018] [core:trace5] [pid 90883] protocol.c(647): [client 10.0.30.15:54280] Request received from client: GET / HTTP/1.1
[Fri Dec 14 13:38:30.248282 2018] [ssl:debug] [pid 90883] ssl_engine_kernel.c(225): [client 10.0.30.15:54280] AH02034: Initial (No.1) HTTPS request received for child 21 (server fe80::c9d0:5dd9:c7ed:2045:443)
[Fri Dec 14 13:38:30.248297 2018] [http:trace4] [pid 90883] http_request.c(312): [client 10.0.30.15:54280] Headers received from client:
[Fri Dec 14 13:38:30.248301 2018] [http:trace4] [pid 90883] http_request.c(316): [client 10.0.30.15:54280]   Host: 10.0.28.168
[Fri Dec 14 13:38:30.248303 2018] [http:trace4] [pid 90883] http_request.c(316): [client 10.0.30.15:54280]   Connection: keep-alive
[Fri Dec 14 13:38:30.248305 2018] [http:trace4] [pid 90883] http_request.c(316): [client 10.0.30.15:54280]   Cache-Control: max-age=0
[Fri Dec 14 13:38:30.248308 2018] [http:trace4] [pid 90883] http_request.c(316): [client 10.0.30.15:54280]   Authorization: Digest username=\\"admin\\", realm=\\"Software Activation\\", nonce=\\"redacted\\", uri=\\"/\\", algorithm=MD5, response=\\"redacted\\", qop=auth, nc=0000002d, cnonce=\\"redacted\\"
[Fri Dec 14 13:38:30.248310 2018] [http:trace4] [pid 90883] http_request.c(316): [client 10.0.30.15:54280]   Upgrade-Insecure-Requests: 1
[Fri Dec 14 13:38:30.248312 2018] [http:trace4] [pid 90883] http_request.c(316): [client 10.0.30.15:54280]   User-Agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.85 Safari/537.36 Vivaldi/2.2.1388.21
[Fri Dec 14 13:38:30.248315 2018] [http:trace4] [pid 90883] http_request.c(316): [client 10.0.30.15:54280]   DNT: 1
[Fri Dec 14 13:38:30.248316 2018] [http:trace4] [pid 90883] http_request.c(316): [client 10.0.30.15:54280]   Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8
[Fri Dec 14 13:38:30.248328 2018] [http:trace4] [pid 90883] http_request.c(316): [client 10.0.30.15:54280]   Accept-Encoding: gzip, deflate, br
[Fri Dec 14 13:38:30.248383 2018] [http:trace4] [pid 90883] http_request.c(316): [client 10.0.30.15:54280]   Accept-Language: sv,en-US;q=0.9,en;q=0.8,nb;q=0.7
[Fri Dec 14 13:38:30.248513 2018] [authz_core:debug] [pid 90883] mod_authz_core.c(835): [client 10.0.30.15:54280] AH01628: authorization result: granted (no directives)
[Fri Dec 14 13:38:30.248542 2018] [core:trace3] [pid 90883] request.c(304): [client 10.0.30.15:54280] request authorized without authentication by access_checker_ex hook: /
[Fri Dec 14 13:38:30.248577 2018] [proxy_http:trace1] [pid 90883] mod_proxy_http.c(60): [client 10.0.30.15:54280] HTTP: canonicalising URL //localhost:6081/
[Fri Dec 14 13:38:30.248640 2018] [proxy:trace2] [pid 90883] proxy_util.c(1985): [client 10.0.30.15:54280] http: found worker http://localhost:6081/ for http://localhost:6081/
[Fri Dec 14 13:38:30.248657 2018] [proxy:debug] [pid 90883] mod_proxy.c(1123): [client 10.0.30.15:54280] AH01143: Running scheme http handler (attempt 0)