Hi James,
I was one of them with the AC measurement problem.
one hint: Page 7 in the Cheat Sheet says:
“Note that AC calculations are inaccurate at buffer depths below 128”
Sample rate is also important!
Here my results of a test on this subject:
input 230V AC 50 Hz (Mains in the Netherlands)
AC Scale 600V Man
Sample rate Hz|Buffer smpl|measured (rounded to 1V)

Hz smpl measured
8000 256 230
8000 128 jumping between 0 and 230 V
8000 64 0
8000 32 0

8000 256 230
4000 256 230, also in AUTO mode
2000 256 230
1000 256 228
500 256 219
250 256 189
125 256 100

125 32 100

2000 256 230
2000 128 230
2000 64 230
2000 32 jumping between 0 and 230V

1000 32 228

~Harm