I have just upgraded our test system to J3.5.1 and find PHP notice - undefined offset : 1 in modules/mod_cmc/helper.php on line 98: and also on line 89.
We still have J3.4.8 on the prod system and with the same action I do not get the notice and everything works. On the test (J3.5.1) system if I enter an email address that is already subscribed I get the message to that effect and do I want to see my profile. When I click on that I do not get the message that an email for update of profile is sent and I don't get the email. When I enter a new email address I do not get the subscription confirmation email. All of this works fine on 3.4.8 and did work before the upgrade on our test system.