Have you taken it apart and cleaned it? Mine acts up every 6 months or so and I'm not sure being dirty is the reason or if I just happened to unknowingly fix the issue while cleaning it out. It always settles down afterward though.
Just an idea...
Edit: Mine is a in sump skimmer. Didn't want to mislead you into thinking I had your model.
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If you can read this thank a Teacher, because its in English thank a Veteran.
110 Gallon FOWLR, 25 Gallon sump/refugium.