I often get dried cracked fingertips during the winter months, but sometimes when my TSH levels fluctuate, my skin does the same. And with PsA, the latter seems to happen not infrequently. So, A., are you currently being treated for hypo/hyper-thyroidism, and B., if so, have you recently had your T4 and TSH levels checked. Aside from that, about the only thing you can do is keep adding a new fingerprint every time your phone begins giving you trouble accepting your current one. And make sure you get the FP recognition with your finger at a lot of different angles.