50 51 Mbps software limit on *.exe - local network

We have network program, on shared SMB2.0 storage.
When avast is active, program loading speed (from network) is 51Mbps and this is constant.
Whit avast disabled, loading speed is ~930Mbps
Same behavior is whit tightVNC network transfer on files.
Avast have some ~50 Mbps limit and it is not processor/ram/ssd bottleneck.
This is for avast 17.2.2517
Is there a fix for this?

Not aware of a bottleneck in the client. Try disabling all shields except the file shield and see if the same issue persists.