Upgraded Sites not applying Culture code when redirecting

We are in the final stages of an upgrade from V9 to V12 (I know we should not be upgrading this many steps at once) and most of the sites seem to be working well, but this issues has me bugged.

We have a custom web bart that switches the culture which worked in V9 but only seems to be working halfway in V12.

The key code is here:

            CultureHelper.SetPreferredCulture(cultureCode);
            CultureHelper.SetPreferredUICultureCode(cultureCode);
            // Force
            Response.Redirect( CurrentDocument.NodeAliasPath, true);

On our sites we have 2 cultures en-US and es-ES. If I attempt to swap to the es-ES from en-US the redirect keeps it on en-US (worked in V9) but going the other way, forcing the es-Es in the url, manual reloading which loads the Spanish site, then selecting English causes it to properly redirect to the English version.

Any suggestions would be welcome.

I have attempted to add the culture code directly into the redirect, but that did not provide any change.