No, most opt-ins are not a problem for SEO, though interstitial popups on mobile devices are not recommended because Google frowns on them, especially if they come up as soon as a user visits a page. In general, we recommend that pop-ups are only shown when a user has either already spent some time on the page (at least 30 seconds), or have scrolled down to at least 50% of the page. Making a good offer that a user cannot refuse is also very important.