Grd radiometric terrain flattening error

I’m having issues with the RTF step in my GRD processing. I’m attaching the error I’m seeing. The images are stack averages of multiple dates, but the stacks and the averages are working well in SNAP (I see no issues with any bands). Before creating stack averages, for each file I:
Applied orbit file > Thermal noise removal > GRD border noise removal > Calibrate to beta nought

Anyone else run into this issue? Any thoughts for how to address it?

Uncheck the Re-grid method here, as it might cause some errors when the DEM resolution is lower than your source image data and you want.