I had not been running G28 between the G29s. I ran into a discussion, either here or in the Marlin github issues, discussing whether or not it was needed for a succession of G29s. I think you were likely a part of that conversation Roxy and I'd like to thank you for discussing your work with Marlin with the rest of us! I have delved into the issues discussion in Marlin's github but often times I feel like I'm missing half the conversation.

I'll give the BeckDac fork a try. One nice thing about Arduino is that changing the firm ware couldn't get much simpler!