Problems showing chart on one client out of 5

I’m experiencing the following problem: I programmed a dialog window where I show a trend. The dialog pops up when I click on a motor: depending on which motor a clicked, the trend will show a different tag pen, which I set on dialog open event. That works perfect on 4 clients out of 5. The 5th client shows no trend, but the Y axis scales correctly, as if data were there. I checked the Java version: on all PCs is Java 1.8.77 running. I tried deleting the client cache in the .ignition user folder, but with no success. Ignition version is 7.8.1

Any suggestion?

Thanks in advance

If I change the IP address on that one client, then it works perfect - I’m sure that there are no duplicated addresses. Even more strange: if I assign that IP address to my PC, then the chart on my PC acting as a client works.