I usually place Nginx or Apache in front of AEM Author to do SSL & Proxy as well as restrict some paths by IP.
Most of the time it works OK, especially on a local network, but lately I'm running into an issue where, via the SSL proxy, only a white page is rendered in AEM Author. For example, when trying to edit a page in Classic UI (by double clicking it in siteadmin).
Most users are on VPN. It seems to happen less frequently in Firefox and more frequently in Chrome.
I can't tell if an Nginx vs an Apache proxy is more likely to result in the issue.
I notice if I use inspect element - network tab - with caching disabled - the page is more likely to render in Chrome.
Sometimes resizing the window with the inspect element - network tab - cache disabled, helps the page to load, or maybe it's just randomly working.
I notice even when only a white screen renders, the network tab of inspect element shows all assets are transferred - it shows each asset, the headers, status, size, and bytes transferred, yet the page is blank.
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You can check if html is loading fine by going to view source by removing /cf# for classic or /editor.html from url. Also check if there are any exceptions in error.log
if the page is loading fine on resizing/or html is present on view source then it might be due to some css or backend exception.
For Chrome, if I do not remove cf# from the URL, there is some source code for the blank page.
If I remove cf# from URL - the page seems to render properly, and there is different source code.
In the error log, if the page renders properly there is more info (i.e., INFO, WARN, ERROR).
If the page only shows a blank screen, only one INFO line added to the error.log (it is one of the same INFO 'resource not found' lines that is also present when the page loads properly).
If inspect element network tab w/ no cache is active, it seems to help the page render properly, even when cf# is present.
I tried directly on port 4502 and can also see the same problem, so this doesn't seem to be proxy related after all. The issue rarely seems to affect Firefox.
I tested this again on a clean AEM 6.5 instance and could not reproduce the issue, I switched the root mapping and default UI to classic - and behind the SSL proxy - I saw no blank pages double clicking sample content in siteadmin - each page opened and rendered fine with cf# sidebar.
The issue I'm experiencing with blank pages is happening on an AEM 6.3-to-6.5 in-place upgraded instance. The info error that shows whether the page loads or is blank is:
10.03.2022 22:30:04.843 *INFO* [10.x.x.x  GET /bin/acs-commons/dynamic-classicui-clientlibs.json HTTP/1.1] org.apache.sling.engine.impl.SlingRequestProcessorImpl service: Resource /bin/acs-commons/dynamic-classicui-clientlibs.json not found
We have not yet updated to an AEM 6.5 supported ACS Commons, currently 3.15 is installed.
One other thing I noticed, when reconfiguring the SAML config in my in-place upgraded instance, the authentication-service system user does not show up under /security/users.html as it does on a clean AEM 6.5 instance. It is still accessible for editing via URL (i.e. /libs/granite/security/content/v2/usereditor.html/home/users/system/authentication-service).
After restarting the in-place upgraded AEM 6.3-to-6.5 instance first thing this morning, for what ever reason, I am not not seeing the issue now. I still see the INFO /bin/acs-commons/dynamic-classicui-clientlibs.json in the log, among others - maybe it's something that only occurs over time, or at certain times of day, maybe network / congestion related, I don't know.