CF2018 and Windows Apache: site-error handler and missing template issues

I've had essentially the same site-wide missing template and error handler setup since CFMX. However, with CF2018, something isn't right.  I'm using Windows Server 2018, Apache 2.4, and CF2018 (w/update9). In past setups, I've had entries like this for CF site-wide missing template and error handlers:

/404error.cfm and /500error.cfm

However, the CF administrator says this (even though these files are in the root folder of my site):

• The file specified as the site wide error handler does not exist. The default error handler will be used until a replacement is created.
• The file specified as the site wide missing template handler does not exist. The default missing template handler will be used until a replacement is created.

Even so, if I request an non-existent cfm page, the expected error page is displayed. 

Apache has error settings in httpd.conf for non-cfm pages like this: 

• ErrorDocument 500 /500error.html
• ErrorDocument 404 /404error.html

However, both my html and cfm error pages have Apache includes to coldfusion content (for banners, sidebars, etc).  If I request an non-existent .html page, I see the expected .html error page, but the included CF shows Tomcat 403 error messages.  If I change the Apache error pages to be the .cfm pages. I just see the Tomcat 403 error page.

I can view the .html error pages directly without any trouble (but they exist and don't have a 404 header).  Tomcat seems to not want to pass the error page to CF when the header gets set by Apache.  If I make a very basic NotFound.html error page and point to that in Apache, it works fine.  However, I'd really prefer for my error page to look like the rest of my site.

I'm having the same problem on both my dev (very simple) and production (vhosts & ssl). Anybody know what's going on here?  What changed and can I fix it?