Made some progress on this now, added an RC filter (500R trimmer and 10p) on the signal and then it locks most of the time. But it seems counter-intuitive that it works when I make the signal worse.
On thing that came to my mind is to lift the signal a little but I will try that next time I am in the lab.
On thing that came to my mind is to lift the signal a little but I will try that next time I am in the lab.
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