MKR GSM not working from LiPo

Hi,
I have an issue with MKR GSM is not working powered only from LiPo. I have tried several LiPos fully charged etc.. MKR working fine from USB, VIN, but not from LiPO.
When USB+LiPo is connected evrything works fine, but when USB is disconnected and the board is powered only form LiPo get freezed probable at GSM operations.
Running only with LiPo freez at GSM.Begin().

Is there any idea what can be done?

THNX
Istvan