I experienced this same issue. I tried every setting to make it work, but it would not. Mirror links (view in browser) and unsubscribe links worked correctly, but not the update_profile, when sent via RSS integration. I contacted customer service, and this was their response (the response time was within a day or so).
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I’ve been informed that the “Update Preferences” form was not designed to work natively with RSS campaigns. However, as a workaround, you can try using the manual scheduling mode (instead of the automatic mode). This will allow you to manually modify the campaign settings and include your update preferences form before sending the campaign out. We’ve shared your scenario with our Campaign/Product team for future improvements, and we sincerely apologize for the limitations you’re experiencing.
In my opinion, this is not a good work around, since the point of RSS campaigns is that they are automatic, not manual.
I could not find any way to link directly to the update profile form, without sending a manual email campaign. My best solution was to add the link to the final email confirmation on subscription signup.
The default template did not allow me to add that link through their builder - it opened in a text only format (so maybe if I knew the proper syntax I could have added the link there). I tried to edit using the simple editor, but that gave no way to add the update_profile link. I tried to manually add that link, but it did not work.
In the end, I created a new template, using the regular template builder, which allowed me to add the update_profile link, and then designated that template for the final confirmation email. This was successful! So I added text to inform the user of the link to update their subscription preference, and suggested to save the email.
Another option I tried was to use automations, to send an email on successful subscription, which also allowed the update profile link and worked correctly. However, once I realized I could add the link to the regular final confirmation email, I did not need the automation.
Hopefully this long explanation saves you the time I wasted exploring all the options!