I don't know if you found an answer to your problem yet. What I've found after months is the PayPal mobile website has something to do with it. I fixed my problem by turning off the fingerprint option in the mobile app, logging out of it, then going to the PayPal mobile website removing the fingerprint option, then re-establishing it. Then going back to the mobile app, entered in my password, it then prompted for the fingerprint and it works after that. Hope this works for someone!
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