I couldn’t identify a gap. Try this as a workaround:
select object
Arrange->Break apart
select all parts
Edit->Auto-join selected shapes
This seems to result in a closed shape. This also tells me that the parts are correctly aligned. I suppose it’s possible that a pair of nodes were not joined although correctly aligned but Edit->Close path should have resolved that condition but did not.
For sure there are some open bugs with path nodes. Another user had an issue where Preview and output would work as expected but display on workspace would not. In that case there was an actual gap in the design but there was clearly an inconsistency between display and output.