Need Solution

Hello,
I am facing problem of data lost after passing thru the data switch.
System architecture is described as below:
PLCs (3 sets)--->RS485/TCP converter ----->Data Switch ------>Control System (DCS).

Data is sent from PLC to DCS. Data is continuosly updates/sent from PLC.
With a laptop, we confirmed all data are healthy before and after RS485/TCP converter. However, data are INTERMITTENTLY updated after the Data Switch.
The data switch is Allied Telesys AT-FSW72 (unmanged)

I am trying to figure out what is causing the data not being updated regularly and your sharing is much appreciated.
what are the parameters i should zoom into.

Thanks.