Sophos XG firewall is blocking the VOICE and Internet traffic

Hi ALL,

We have deployed the Sophos XG firewall with 17.5.9 MR-09 firmware. I have created Internet access policy, DNS policy, and 03 firewall groups.  In these 03 groups only firewall categories are selected as an access level. It has worked for 03 hours without any issue. I have tried to access the allowed website but sometimes these are accessible and sometimes these are not. VOICE traffic starts getting dropped. 

I have tried to ping global DNS 8.8.8.8 it is giving RTOs on a random order. At the same time i have watched the logs through the GUI log viewer , where i have saw the denied traffic a lot, that some of our broadcast traffic  and some are from outside our network. 

All these events are occurring at the same time, but if i ping the dns 8.8.8.8 from the firewall console, it pings the dns without any RTO.

We are using two internet lines here, one is primary and another one is as secondary.

If we shift the same LAN network on the TP-link router, it works without any issue. please suggest, how could it be resolved?

Thanks!

Regards:

Vinay Pal