I get various "missing" CutPlane Markers frequently -- there doesn't seem to be anything missing (I assumed they had to do with my CadImage add-ons), and I've learned to ignore the warning.
MacBook Pro Apple M2 Max, 96 GB of RAM
AC27 US (5003) on Mac OS Ventura 13.6.2
Started on AC4.0 in 91/92/93; full-time user since AC8.1 in 2004