I corrected it by doing a search in Sigil for the address class which created the error.
This is an example of the code.
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I took the</span></p>
<address class="calibre5">
<span face="Times New Roman">George Washington Parkway</span>
</address>
<p><span face="Times New Roman">, heading toward the Helms compound north of</span> <span face="Times New Roman">Georgetown</span> <span face="Times New Roman">.<span> </span> Traffic was thick.<span> </span> National Public Radio seeped through the stereo speakers, the announcer’s velvety tones like an antidote to road rage.</span></p>
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The original text as a mobi looks like normal text, but in calibre it is transformed into <address class="calibre5">, with line break before and after created. I did a search and replace which cured the problem in this ebook.
Could anyone look at the original to see if there is something in the mobi coding? I could upload the mobi file as a private attachment.