@mhossain I believe this testing shows it to be mostly a network problem. You may want to get a service group in to inspect your network if you do not have the expertise on staff to investigate it. Hope you can get it fixed.
This is happening in our environment too. Did you ever resolve this?
I would agree with @jeowings that this is network or possibly authentication. We have an office on an vpn connection and they will all sometimes go offline and then all come back. Another issue can be a nic or switch dropout. Try to find the commonality of the affected PCs and review their event logs.
We also have this issue when a user waits until they are forced to change their password.
For us, it seems to be any client that is not on the same VLAN as the epicor server. Every other service we use works on that VLAN. It’s only epicor that drops. My fix it change the Epicor users to the same VLAN as the epicor server, but it’s not really what we want.