Source formatting on longer documents (DW '17)

Hello,

Apologies if asked before -did not find anything related.

I keep a bunch of 'old' static documents online, containing up to 60 pages of printed text in each document.

When I want to use the Source Formatting feature in DW '17, it does not seem to work for the complete document.  It works smoothly when selecting a paragraph, a list etc.

Hence my question: is there a limit to the Source Formatting feature (which I use very often) - I seem to remember that it worked in previous DW versions but am not sure.

Thank you for advising and kind regards,

Michel.