Thank you! Oddly, with all the photos and the original spreadsheet you sent, I didn’t have any issues with it accepting the import. It also didn’t have any blue cells in the preview.
Sometimes bulk import doesn’t like something about an Excel format, whether it’s a cell type or something else that’s not about the data you’ve entered. In the past, I’ve suggested to users to save the file as a .csv and then convert it back to .xlsx. That tends to strip away anything that it may have disliked about cell formats.
I think using the workaround to re-save the same file as we did before will be your best way forward for now since I’m not able to consistently reproduce the original issue.