A system administrator noticed that all iOS devices in the medical facility he had been working at stopped working after a recent installation of an MRI machine. Turns out this was not related to any electromagnetic interference, but rather helium of all things. Below is one of the most interesting things I have ever read about electronics:
Follow-up with some interesting comments from other people who have had strange bugs that were also hard to track down: https://www.reddit.com/r/sysadmin/comments/9si6r9/postmortem_mri_disables_every_ios_device_in/
The tl;dr is that there was a helium leak during the setup of the MRI. MRIs use very large, powerful magnets and liquid helium is used to cool them. The coolant was leaking which spread into the HVAC system in the facility. Many iOS devices use MEMS oscillators to generate a clock signal rather than using quartz. This is for packaging and cost saving reasons since they are smaller (thinner) and cheaper than a standard quartz oscillator. Quartz oscillators are hermetically sealed in metal to prevent interference but MEMS oscillators are usually sealed in plastic. Helium can permeate through plastic leading to the interference with clock signal, and since the clock signal is vital to numerous parts of an IC, the iOS devices stopped working. I do recommend reading the entire post though, it’s super interesting.