I have protected my column headings in a spreadsheet that I am sharing, so collaborators can't edit them.
Now, when you share your spreadsheet with any one, and have some protected ranges in it, then that viewer or editor is facing problem to read the data of those protected cells.
Have a look at the screenshot below:
Here is the solution, ask your collaborator (or viewer or editor) to uncheck "Protected ranges" from "View" menu. After they uncheck it then these protected cells would be clearly visible to them.
Have a look at the animated screenshot below:
I hope the above solution will help you, and if you need more help then please do comment below on this blog itself, I will try to help you out.