When you open xlsx file containing comments you see that all comments are shown (visible).
You can hide all comments one by one (as there's no interface option "Hide All Comments") and save file in the current format (xlsx).
But after reopening this file you see that all comments are shown again.
The only workaround is to hide comments one by one and save file in ods or xls.
This is a regression, as LO 3.4.5 showed comments in xlsx correctly.
Created attachment 60623 [details]
Original file containing comments
By default comments in this file are hidden (when opening in Excel 2010 or Excel Viewer). When you open this file in 3.5.1,3.5.2, 184.108.40.206 all comments are shown. When you open in 3.4.5 comments are hidden.
*** This bug has been marked as a duplicate of bug 47904 ***