Some HTML breaks spell checking in DW 20.2?

I am having issues with getting spell check to work for certian HTML documents. DW 20.2 build 15263 

I have certain documents that, in Design view, present a blank white window. They look fine in Live mode.

When I try to spell check the documents that produce the blank white window (mindful that spell check works only in Design view) I get a dialouge box that says "Spelling check complete." The trouble is that no spelling check has taken place because none of the mispelled words in the document are flagged.

I have created a simple HTML document as a test. That document does appear appropriately in Design view and spell check will flag mis-spelled words in it as it should. 

So I guess that

1) Some aspect of the code in the files that present a blank white window in Design view is breaking Design view.

2) Spell check is not working when/because Design view is broken.

I'll note that one the troublesome files makes use of Google fonts and when I select Design view I get a note that says "Web Fonts are not rendered in Design view. Please switch to Live view to preview Web Fonts", however I can create a test file that uses Google fonts that does not generate that note and for which spell check works.

I very much need spell check to work and this circumstance is rather frustrating and suprising behaviour in a application as mature as Dreamweaver. When DM says a spell check have been completed I need to be able to believe that.

Can anyone explain what might be going on and steps to remedy? What HTML code might break Design view? Any help greatfully received.