Unfortunately I am only able to test on the Oneplus One at the moment, my Nexus 5 experienced a soldering iron-related hardware failure. I have a new motherboard in the mail (again, at my expense 😉 ).
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Everything seems fine here. I wonder if the calling issues you're experiencing are related to an interaction between Ubuntu Touch, the Nexus 5, and your carrier. I can say that I used a Nexus 5 daily for 7 months on an AT&T MVNO and only missed a call when I had it muted (that is, because I was a dumbbell, not the phone).
Since this has deviated from the "Please help revive my Nexus 5" topic, I'd like to ask you to open a new thread to discuss this problem. Please include information like your carrier and any patterns you've found between when calls work or do not work.