Hello @Dustin_Rumburg Dustin,
Welcome to the B&R Community!
You can find the standards met within a magnetic field, in the International and National Certifications section of the T50 User’s Manual (AS Help link below). Testing beyond the standards is not publicly available information from B&R, so there won’t be an official statement about the strongest magnetic field a device can withstand or how the device fails within such a field.
T50 Immunity Requirements Standards - B&R Online Help (br-automation.com)