The first thing to try is looking at the imported details which are accessed via import/export - import pay list. The right-hand side of the screen will show imported files, and a date filed. This corresponds to the date the file was uploaded.
The left-hand side will be the corresponding payroll report details indicated by a logged date. This logged date should correspond to the date filed date. If you have files showing on the right that have no corresponding details on the left e.g. date filed dates with no logged date matching it, this indicates that the file has imported but not processed. This scenario can block further file imports.
📌Note: If this occurs, use the remote data button on the right-hand side for any entries that have a date filed date, with no corresponding logged date on the left-hand side. You can then try and upload the file from payroll again.