When this story first broke I remember seeing two interviews where two different protagonists were asked "What evidence do you have?" several times each. Both answered to the effect that 'questions must be answered'. Neither offered any evidence.

This leaves two possibilities. Either there is no evidence or neither interviewee wanted to reveal what evidence they had. The echo chamber here will discount the first possibility so let's look at the second. They were unwilling to reveal their evidence. To me that also leaves two possibilities and one of them is that they don't actually have any. They are just throwing mud at the wall knowing that some of it will stick, for a while at least. The other possibility is that whatever evidence they have is so weak that it will not stand up to widespread scrutiny.

The electoral commission has looked at this case twice already and found nothing wrong. Perhaps they are just hoping for third time lucky.