The I2C components are on a custom shield directly mounted to the Arduino, so the wires are less than 1-2” max from component to pin.
I did a lot more testing. With a small 10ms delay following SD writes my setup is bulletproof running for eight hours straight...sampling, writing to SD occasionally, transmitting on the radio, etc. The sampling is at 50Hz, so that is as close to perfect as I can get over eight hours. Adding the level shifters also seemed to fix the radio interference causing lock-ups. I was prepared to build a faraday cage around the Arduino, but now it seems like I don’t need to.
I’ll put an oscilloscope on the pins and see if anything looks unusual during radio transmission.
Thanks!