Hi Paola,
I have seen a lot of the same problems, and the only way is to resend the BP by request load in R3AR4 or resend by CRMM_BUPA_MAP after correcting the error which caused the failure.
It is standard design that if you change the customer, the task will be "U". The task "I" is only used when customer is created. If you send by request, the task will be "M".
Pleas see KBA:
1859605 - Bdoc R11124 during BP transfer from ERP to CRM
Best Regards,
Ellen