Voatz, for example, gives each voter an anonymized identification number that allows them to look up their votes as they were recorded on the Voatz server. This is probably essential for ensuring that votes are recorded correctly. But it erodes the sanctity of the private ballot, since people in positions of power could coerce voters into revealing how they voted.
I immediately think that this could be fixed by giving voters the opportunity to generate multiple ID numbers that lead to “proof” that the voter a different way. Maybe even different passwords that lead to only one voting record, in the event of someone forcing you to log in and show that you voted the way they told you. There are probably other attacks that can be performed upon this vague handwavy scheme of course.
Can’t fix the incredibly stupid name of “Voatz” though, I cringe every time I see them mentioned.