Does your conversion of &nbsp; work? also you may get spurious mulit-spaces, esp if there was &nbsp;&nbsp;<hr>&nbsp;&nbsp; in the string.

So i'd put the 'clear multi-spaces' step last in that group to cover that, as for that step...
any of

$description =~ s/\s*/ /s;
$description =~ s/\s+/ /s;
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should work AFAIK, i don't think the 's' modifier at the end is strictly needed, Which variation have you tried? And are you just trying to replace multi-spaces with single ones at that step? Try a debug by replacing with a hyphen instead?

Perhaps more questions than answers, but may be of some use?!