Issue with Smart Search and indexing - error: date.getTime is not a function

Hi - I am getting this error in the Librarys for Smart Search. 

I am a bit unsure where the error resides - it is a KMUpdate error. 

image.png

I have never seen it before - this is while testing an updgrade from 9.41 to 9.52. 

Any clue? 

BR Ivis.