Hub issues : loosing message between devices and PC with TCP/IP connection

Hub issues : loosing message between devices and PC with TCP/IP connection

I have customized controller. AVR board has tcp/ip module(chip) in order
to communicate with PCs. PC has 4 channels netwrok card. each channel has
connected to Hub. each Hub has connected to 10 controllers.
PC has connected almost 50 controllers totally. Sometimes I have a time
out error which means no ACK message. If I have several times time out
error, then connection was loosed. I can't connect to that controller
again. Should be power reset. then It connects again.
If I connect to controller directly without hub, then there is no more
time out error.
I'm looking for what is the root cause for this happening. loosing
message, how to monitor where the message loose ? PC, Hub, and customized
controller...
wireShark tool is helpful to find the root cause or not ?