Thanks to Dave for drawing this to my attention.
Groom, P. 2006 Erosion Control Works at Waun Maun Standing Stones SAM Pe124
I had assumed that Waun Mawn was not a Scheduled Ancient Monument, but it appears that it is! The number is SAM Pe124. That means that Cadw must have had some involvement in the consent and monitoring process for the digs on the site in 2017 and 2018. I shall try to find out what the consent process was (and is) and ask them what they thought of the state of the site when the diggers departed.......