If there is a tile flagged with "Missing Stemcell" in Tanzu Operations Manager Stemcell library page then you will not be able to save any changes. Clicking save when a product has a "Missing Stemcell" flag will result in an HTTP 500 error and the page will not show any content unless you refresh the page.
Operations Manager 3.0.41
This is a known bug and will be fixed in a later version of Operations Manager. To workaround this simply upload all missing Stemcells before making changes in the Stemcell library page.