I'm setting up a private wiki under a subdomain of a domain my company uses for wikis on AWS. I just purchased the MediaWiki instance from the AWS marketplace and have been working to just get the wiki up and running including setting up the admin account passwords, installing a Let's Encrypt cert for HTTPS, and disabling access to anonymous users. I was testing to verify that this works when I ran into an issue: upon successful login, a blank "Log in" page is shown instead of redirecting to the original destination.
So first I go to https://private.example.com/index.php/Main_Page and get a "Login required" page with a link to log in. This is expected.
When I click on the link, I get sent to https://private.example.com/index.php?title=Special:UserLogin&returnto=Main+Page&returntoquery= with the title "Log in" and the log in form, which looks good so far.
However when I enter in the admin username and password and submit, I expect to be redirected back to https://private.example.com/index.php/Main_Page with the content visible, but instead I get redirected to https://private.example.com/index.php?title=Special:UserLogin&returnto=Main+Page with the title "Log in" and no body. I've tried this on a different browser to see if it is some sort of caching issue, but I get the same results there too.
Since I've done almost nothing, I don't know what I could have done to cause this. Is there a configuration that I either failed to setup correctly or perhaps corrupted that might cause this? Could it be related to the wiki having a subdomain URL?