Taken from blizzard
hope this helps
“There could be a couple of things happening here typically it comes down to a connection issue of some sort, or interference/corruption caused by other software/permission issues on the system.
Try doing a power cycle on your system. Turn off all devices including the modem. Wait 60 seconds, turn on the modem, wait 5 minutes, turn on any network devices, wait 2 minutes, turn on your computer and try the game.
Sometimes firewall or routing software/hardware will have some advanced settings to prioritize and manage types of network traffic. Normally that is not an issue but we have seen situations where it can interfere with the delivery of the data for our games/voice chat.
Let’s try turning off these features:
QoS
SIP ALG
RoG (ASUS Routers Only)
Security firewalls (Some ISP provided modems)
Not all devices will have these options and the steps for turning these functions off will be different depending on the make/model/software version of the devices and programs involved. If necessary look at the documentation for your security and routing products to find out how to turn these options off”