Voltage Translator (SN74LVC1T45) Locking Up?
This turned out to be caused by insufficiently heated solder paste on one of the pins on the chip.  I removed the chip, checked for bridges, cleaned out the pads and re-soldered and now the data is coming back clean. Strange that it only affected the circuit when running at 3.3v and only partway through the communication. Perhaps increased capacitance on the input or higher resistance making for weak hi/low transitions.