Excel Add-in (Office.js) sometimes disappeared from Excel ribbon

Question

Generally when we open excel sheet our custom add-ins automatically appears on Ribbon. However, on multiple occasions, when opening an excel sheet, the Add-Ins which are deployed on Office 365 Add-In's catalog does not appears on ribbon. The Excel add-in failed to load altogether. This is an intermittent issue. Only few times we see this add-in behavior on excel open. Please let us know in case you came across similar behavior/observations on custom add-ins.