I have the exact same problem. I tested it more than 10 times. Half of the time it was fine but sometimes it couldn't smoothly track my finger but had LOTS of interruptions in the yellow lines. They have a new firmware update that's being rolled out. It's supposed to have some bugfixes, let's hope this is one if them. I've encountered this problem a lot now but whenever I restart the phone it's fine, which I'm hoping means it's just a software problem. The update is supposed to contain some changes to screen calibration, so who knows. Gonna try and be optimistic.
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