It looks like that output is incomplete. What was at the very bottom? That's where the interesting stuff would be.
However, since I wrote that warning in the codebase, I think I got a better insight to what the issue is: the McASP (multi-channel audio serial port, basically an I2S bus) encounters an error of some sorts and blocks, and should be re-inited. This wouldn't normally show any useful message in
dmesg. We implemented some code on the PRU firmware for the CTAG to automatically recover from such errors, but this has not yet made its way back into the firmware for the regular Bela. Implementing such auto-recovery would still cause an audible glitch on the audio, but wouldn't crash the program.
What is most interesting is the cause of these errors: when I observed them, they don't occur during normal operation, but they occur when there is some sort of voltage spike on the power rails. For instance, if your I2C peripherals or LEDs are taking lots of current, this could cause a spike on the 3.3V power rail, which may not be enough to cause troubles to Linux (e.g.: sometimes this would cause the eMMC or SD card to remount as read-only, requiring a reboot), but still would inject enough noise on the McASP circuitry to cause this temporary error.
If this is the case, ideally, you would use the "SYS 5V" (P9.05/06) pin for anything that requires a sensible amount of current (also, you should power the BeagleBone through the barrel jack). If you really need to use the 3.3V supply (e.g.: because your I2C drivers use the same supply for Vdd and the output signal), then try to add some capacitors on the power rail next to the load (or use some 3.3V to 5V level shifters for the I2C, as suggested
Another case when this McASP underrun happens (I think) is if you send a fairly high voltage signal into the audio input (e.g.: by plugging a piezo disk straight in and hitting it hard). In this case, you'd have to attenuate the piezo signal.