bash 30 second delay when checking if file exists

I have a file system that is shared between several computers. I cannot open network connections between these computers so I have written a program to communicate via files. I have a server that checks a folder for the appearance of instruction files, it reads, executes and writes an output file and then creates a signal file to indicate the file is ready.

to check for a file with a while loop

while [[ ! -e $READY_FILE ]]
  do sleep 1
done
do something

The server gets and processes the file pretty much right away and makes the signal file but I am seeing a strange latency on the client side.

when the server and client are running on the same machine the latency is very low. When I run the client on a separate computer the latency is around 30 seconds.

time bash client.sh -f commands.txt
done

real    0m31.945s
user    0m0.048s
sys     0m0.314s

This is reproducible +/- 2 seconds.

I can kill the problem by making the client computer do anything with the working directory.

time bash client.sh -f commands.txt & sleep 5; ls $wd >/dev/null

real    0m5.120s
user    0m0.014s
sys     0m0.083s

time bash client.sh -f commands.txt & sleep 3.5; ls $wd >/dev/null

real    0m3.749s
user    0m0.011s
sys     0m0.055s

I can correct it in the program by changing the while loop to

while [[ ! -e $READY_FILE ]]
  do ls $wd >/dev/null
  sleep 1
done

Now i get

time bash client.sh -f commands.txt

real    0m1.075s
user    0m0.004s
sys     0m0.056s

My question is why is there a 30 second delay for the test [[ -e $READY_FILE ]] to detect the file?