Hi BP101, our device is bus powered so we haven't connected PB1 to VBUS. If the code is running we must have power connected and when the power is removed the code doesn't run ;) . In our case, and on three different systems (two Tiva dev kits from TI and one prototype board of our own design) using two different variants of the TM4C129 family of processors and different 3V3 regulators we see the 3V3 rail pulled down to about 0.1V. In each case the regulator is current limiting to between 300mA and 600mA (inferred from device specs, not measured). It is quite unlikely to be a dry joint on each system or a common failure mode of the regulators.
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