Rollershutter items may or may not understand percentage commands, only UP, DOWN, STOP.
The slider in HABPanel cannot send those, to do that you need to either:
- use a set of buttons (align 2 or 3 of them and configure them to send UP/STOP/DOWN), like in the demo here: http://demo.openhab.org:8080/habpanel/index.html#/view/ground-floor
- use one of the community widgets for rollershutters/blinds, you can find them in the in-app gallery:
Rollershutter simple
Widget: Blinds - build your own