Payment not going through

Does anybody else experience this:

1- Some payments are ok, in the order manager it shows as paid and completed.

2- Sometimes the order appears 2 times in order manager, one time awaiting payment and the second time paid and completed. The payment goes through to Paypal

3- Sometimes it shows awaiting payment and the payment is not transferred to Paypal so we lose customers!!!!

No settings were changed so WHY I lost 2 customers today not talking about the others???

Please help