Loop_out does't work with mask shape keyframes?

Hi all. I'm trying to loop a mask shape animation. However, the usual
loop_out("cycle",0) is not working. I'm getting a "loop is not
supported for custom properties" error.

It looks like the loop functions don't work on Source Text either.

Something like this should be close:

if (numKeys > 1){
  tOut = key(numKeys).time;
  if (time > tOut){
    tIn = key(numKeys - 1).time;
    tDur = tOut - tIn;
    t = (time - tOut)%tDur - thisComp.frameDuration;
    valueAtTime(tIn + t);
  }else
}else

You should also be able do it with time remapping and a loop expression.