The last vote that SecurePoll allowed was at 18:34, 17 January 2023, which is pretty much exactly the timing of T327196: 2023-01-17 Wikimedia full site outage. I think this probably indicates that that outage impacted votewiki's central list.
All subsequent voters were manually added to the eligibility list.
See also comments on T326408 where we were talking about it prior to this task.