Feedback of buttons in HABPanel is gone

Hi there,

I have been using OpenHAB and HABPanel for a long time now. I am still on OpenHAB 2.5.10-1.

Since some weeks I have a strange behaviour: The buttons in my HABPanel do not give me any feedback anymore when pressed. In the past I actually saw visually when I pressed a button. Now when pressing a button visually nothing happens.

This is on my tablet with Google Chrome and on a Workstation with Mozilla Firefox.

Does anybody know what could be the root of this problem?

Best regards,