I first discovered that the "Insert Cut Cells" option was appearing inconsistently on legacy excel files after having upgraded to 365. I worked through several steps of troubleshooting to pick through the details to discover exactly why that was the case for one of my files.
I have read through all many pages of content with similar comments on Copy/Paste functions in Excel no longer behaving as expected after upgrading to 365. I am disappointed in replies that declare they have the answer, when in fact they have found yet another way in which it is behaving differently than before the upgrade. Worse are those that make it about the user. This is clearly a programming issue and I have full confidence that Microsoft will identify it, work through it, and issue an update. In the meantime, if you cannot find the issue you have within the many threads on this subject already, please identify and document the specifics of the particular situation that you are encountering so that MS can hone in on the root cause on their end.
NOTE: Making the Clipboard visible was a huge time-saver in troubleshooting. This was suggested on another thread, and I highly recommend it for clarity and sanity as you test your own variables.
My particular issue is in relation to an Excel file utilizing Data Validation in a column that requires the use of a LIST (dropdown). Nothing particularly complicated. Whether cutting or copying, the paste options that are available, do no include pasting what I have copied into a new row or copying over an existing row while there is a cell that contains a dropdown. I created a named range of values for the Source of the dropdown list. The error code that appears is "This action won't work on multiple selections."
Starting over with a newly created file with all of the same complexity, plus the same dropdown artifact eliminates this error. While that is useful information, it is not a solution in itself, as I am certain that Microsoft will not just tell all of the business users of the modern world to rebuild all of their complex spreadsheets over again. The ROI for recreation suddenly makes switching to other software viable, where in contrast, having working legacy files are a reason to NEVER switch - it is part of the strength.
Thread users, thank you for sharing problems and solutions so openly. Microsoft, thank you for being focused on continual improvement through this style of forum.