Help HTC 10 transparent bubble

[mmorganjones]

HTC 10 6.0.1 MARSHMALLOW. Recently noticed a small transparent half circle bubble against the side of the screen (portrait) and becomes a full bubble in landscape mode. Doesn't seem to do anything. Any ideas on what it is or how to get rid if it. Cheers
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[mikedt]

Looks like a floating widget from something. Have you got Clean Master installed, because I'm sure that can do it.