TCP/IP data loss

[shantanu@india]

Hi,
I'm using a TCP/IP to RS485 converter ATC1000 to fetch data from a PIC to PC. The communication is at 9600baud on the 485 side and the Ethernet cable is connected to a WiFi router which is connected to the PC.
The PIC transmits 16 bytes to the SCADA software against a request. The TCP read timeout is set at 500 msec.
The problem is some packets are not being delivered in time causing some missing records. Say out of 200 successful receptions 4/5 receptions are unsuccessful.
People are using the Wifi to access internet and watch YouTube etc.
Can that be a reason?