Doubled Registration

We are using the free version of RegistrationMagic for a church-related youth event.

Unfortunately, some of the registrations are send in twice or even three times eventhough our participants only confirm the registration in the frontend once.
The second or third registration per attendee do sometimes arrive with an delay of some hours, sometimes already some minutes after the actual registration.
Furthermore, the second/third registration is missing the appendix whenever one was included in the first registration, while all other data is included.

How could this issue be fixed? Has it appeared be before?