Endnotes as superscript when placed manually reverted to regular type

InDesign 17.4 — manually placed endnotes appeared correctly in text blocks as superscript. After the file was saved, closed, and then reopened the superscript formatting was gone. All of the endnotes appear to still be recognized as such by the program, i.e. if one is deleted the numbering is adjusted. Have I missed a setting? I have had to go through the text an manually format each as superscript. Lucky for me that I discovered this on a short piece, but I have plans for a larger document and this would be a disaster to correct.