I apologize for my incompetence. Here is the link to the Adafruit forum where I first posted my question:
https://forums.adafruit.com/viewtopic.php?f=57&t=127764
There is much more information there than I could post on this forum.
Have you read the complete tutorial, to make the FeatherWing work ?
I have read the tutorial for the Feather Wing RFM69HCW 900MHZ, and the Feather Wing has worked reliably well in other sketches that I used. In those sketches, I did not use the ISR, but instead I used the micros() function to perform the data calculations that I otherwise performed in the ISR. However, for some unknown reason, in those micros() sketches sometimes the sketch would lock up after a few hours, but most of the time it would run for hours without a problem. A friend (much more knowledgeable than I) recommended that I use the ISR instead of the micros().
Does the Adafruit board software not work with Arduino IDE 1.8.5 ? Can you please update your Arduino IDE.
I will definitely try to update the Arduino IDE to 1.8.5 and see if that works. Thanks for the advice.
That sort of thing can happen when you run out of memory
My transmitter sketch is using 35,964 bytes (13%) out of 262,144 bytes.
Use serial print statements to see where your loop function is stalling
The loop function does not stall when I use the serial monitor display, but only when I use the micro SD. Just to make sure that I understand what you are advising (I apologize for my ignorance), should I use dataFile.print statements to the SD, and place them throughout the loop function to see which print statement is printed to the SD card just before the loop function stalls?