VS-GGU-E2M0400 Random Drop Calls

Hi.
I'm new with the openstack.
I made the whole configuration based on my voip knowledge and everything is working as expected, however, a problem appeared after putting the equipment into production. Randomly some calls are terminated in a short time, less than 2 minutes for no reason. I checked signal, cables, settings, I do not use any type of charging.
I do not know what to do or how to proceed to determine what is happening. I need some help to know what kind of logging I can enable to give me the info of why this calls are been droped and how to fix this.

My equipment is:
Model: VS-GGU-E2M0400
Version: 2.3.5 (before was 2.3.8 but the seller asked me to downgrade)

Hi sir,
sorry about this issue, please add my skype. i will help you check.
skype john.sun : live:e172816a6bbf5220

cant find you on skype. could u add me? daniel.echizen

Hi sir,
ok i already add you, please receive.