I do wonder about that last text sent to Jen too, about the twelve shifts in a row Claudia was last minute drafted in to work. Which was sent Wednesday evening. I think this is too soon to have her phone taken over outright by the perps and was sent before the phonecalls w her parents (?) unless they text and deleted from her outbox before she noticed, only surely they'd reasonably expect a reply that would puzzle her, increasing the likelihood that if this is what happened Jen or someone with access to her phone either text themselves from Claudia's or if elsewhere was clued up to respond immediately for the other person to then delete, perhaps knowing investigators wouldn't be able to tell provided they don't find the phone (accurate??)
My gut instinct is that if term began March 20th the previous week or two had probs been relatively chilled at work, another possible reason why she was out and about more in the evening times. Could the smaller numbers mean aspects of her job changed temporarily, that she worked in different buildings, which might explain the mixed reporting, meaning perhaps she met someone that way? What about new staff at work?
A bit more out there ofc but aside from building, what other work/tests were being carried out around the uni grounds in Heslington during student holidays? York Uni's Physics and Engineering depts are renowned for their research and innovation, with ties to new arms and military tech development. Who knows a lovers tiff or something more serious that led to silence could have brought her in the path of a ray gun test of some description. Never underestimate the determination of nerds to not face justice!!