Be sure to check your clean source settings. Setting it to clean upon "Open" just may restore the functionality you're accustomed to.
I think it's a little confusing because people are thinking that entities are disappearing, when in fact, their are no actual nbsp entities in the odt output. Only special characters that some software has been known to silently convert to a named entity. For better or worse (individuals will have to decide for themselves), Sigil is moving toward NOT making any silent changes to code.
But do try the different clean source settings of Sigil to see if they have any bearing on your situation.
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