Not logging all form entries? Authorize.net account does not match.

I installed GF + Authorize.net add on for a client recently. The client says that their Authorize.net account is showing more entries than those logged in the GF database table; ergo GF is not logging all form entries:

"The problem is that the forms are displaying X number of donation
entries in our database, but the merchant account with authorize.net is
showing X+Y entries, meaning that our database with Gravity Forms is not
logging all of the entries. There is no display message, we see it when we
compare the two records between gravity forms and authorize.net."

they assume that if the records don't match, then GF is not logging all entries. I think it also stands to reason that transactions are happening outside of the Gravity form - does that sound right? I don't know where/how those transactions would be made, though. All Any insights into how to troubleshoot this issue would be appreciated.

ETA:
Here is the Web link -
https://www.isgh.org/donate/

Is there a way to demonstrate this? They are convinced that GF is not logging all form submissions (which does not sound at all right to me). Is there anythng specific they can ask authorize.net to determine how a transaction took place? Sorry if this sounds ignorant - I don't use authorize.net myself and so am just trying to follow up on their complaint. Thanks!