2,23,6 markFormatter change?

[Paul Scott]

2.23.6

I have been using the following definition for many years:

CircleNumberMark = {
  \set Score.markFormatter = #format-mark-circle-numbers
}

I now get:

warning: cannot find property type-check for `markFormatter' 
(translation-type?).  perhaps a typing error?

from one score where I may have made an unknown change but also from a 
score which hasn't changed

I have looked at the 2,23,6 changes.

TIA for any ideas before I do extensive problem solving,

Paul