I have been using excel for years to handle large amounts of data. Recently, I have noticed if I paste a value over multiple rows, it will paste into the rows that I have filtered out and not only into rows that are seen. This is occurring both on the web version and desktop version of excel. I rely heavily on this action and I am not sure what has changed. Does anyone have any ideas?
The reason why data scientists generally despise Excel is exactly what you encounter. It is not reproducible, error-prone, sometimes changes gene names to dates, does a lot of goofy things, and is generally a pita.
If you want to properly and reproducibly handle (large) data then learn a programming language such as R or Python. This is what this forum can help with. Debugging commercial GUIs is not on-topic here.