Newest vers. dropping subdomain?

I seem to have an interesting issue.

The newest version of WordPress drops the subdomain back to the main page, while the older version doesn’t.

IE:
https://singalong.astralromance.com (which is the subdomain of https://astralromance.com/singalong/) wont work (it drops it to https://astralromance.com) however, https://typodemon.astralromance.com (which is the subdomain of https://astralromance.com/typodemon/) does work, and notably the wordpress used on typodemon is an older version. (also, now that I’ve noticed it https://astralromance.com/typodemon/ tries to force it to typodemon.astralromance.com … oy…)

Is there some magic way I have to handle it to get this newer version of wordpress to work properly? I’ve never had a problem before, either setting up WordPress via cpanel or installing it manually, so never had to fiddle with anything.

ALSO, the subdomain WORKS so long as I don’t point it to index.php.
So going to https://singalong.astralromance.com/wp-login.php works just fine and dandy (though if you try to login that way, the following error pops up:
ERROR: WordPress requires Cookies but your browser does not support them or they are blocked).

And yes, my cookies are turned on and supported.