That’s a very helpful diagnostic, and I will no longer suspect the Embedded edition!
Given your input Phil, and now that I have an alternative pfSense appliance at my client site, I am going to completely re-install pfSense on my first device to see if the PPPoE problem is magically fixed by a fresh re-install. I anticipate that a re-install will not fix the problem, but I want to put a nail in that coffin because it may be suggested or requested by a pfSense developer.
Out of curiosity Phil, what is the make of the WAN interface on your problematic unit (e.g., Intel, Broadcom, etc.)? I may be overlooking this information in your PPP log.