Rows being moved and groups of entries in columns become gibberish

Using Excel 365, current version. Longtime Excel user.  Saving frequently.  Rows, usually more than one, are being moved intact to other places on the spreadsheet.  Data in columns randomly become gibberish usually in blocks of several entries.  An "x" placed in a column is repeated in that column beneath the end of the file.  What in the world is going on?  HELP!