Code sent to gmail while using gmail..!

Lemmy, a few minutes ago I tried to change my notification settings for a website, but it was not possible using Gmail:

From my phone email inbox I clicked the link to unsubscribe. This opens the website, but via the gmail app. To sign into the website, they sent a single-use sign in code to my email... which I can't access because I'm using the email app to view the website. If I exit the website to view the new email containing the code, then I will lose my place on the site and need a new code sent to sign in. Thus an unresolvable loop.

Is this an asinine gmail issue, or am I an idiot? Please advise. I have ended up staying subscribed to several extremely annoying websites because of this bug/tactic.