Numbers spreadsheet "may look different."

That is an image bullet. You can go looking for it to see if it is there in the application package. Don't go messing around with anything in there though unless you know what you are doing.

1. Applications folder
2. Right click on the Numbers app and choose "Show package contents"
3. Go to the Resources->ImageBullets folder
4. That image file should be there. If it is, click on it and see if it opens in the Preview app. If it is not or if it does not open, that verifies the problem.

The bullet is light gray circular shape with a curvy line across it. You might be using it as an image bullet for a list of items in a cell. I'd post a fresh copy of it for you but the link to it will get taken down by the moderator so I'm not going to bother trying. In any case, you might be better off deleting the Numbers app and reinstalling it because other things may also be missing/damaged.

Or you can probably get around this particular problem by finding the offending bullet image(s) in your spreadsheet and replacing it/them with a different one. That would be done in the Text tab of the sidebar down at the bottom where it has bullets and lists.

To see what would happen, I made a document that used that image bullet, saved it, quit Numbers, then removed the bullet from the Numbers app package. I opened the document after that with no problem and the bullets I had previously made were still there but that particular bullet image was no longer an option for new bullets. I then made a new document and was able to copy/paste text with that image bullet into that document. I am now assuming Numbers makes the image part of the document and it is that copy of it that is corrupted.

So, here are some ideas:

I would look for all multi-line text in your document where image bullets might have been (they may not be visible now because the image is corrupted) and assign them a different bullet than that one. Once they are all gone you could try applying the old bullet again and it might get a good copy from the Numbers app package.

Or make some multi-line text in a cell and apply that image bullet to it to see if it works. Maybe it will overwrite the corrupted version in the document (or maybe it won't work either).

Or create a new document that uses that image bullet. Copy/paste that text (and bullet) into your corrupted document. Maybe that will copy a good version of it.

Those ideas are not all mutually exclusive, it might take a combination of them or maybe none of it will work. Maybe if you remove all instances of the corrupted image bullet it will discard the image from the file.

Excel does not support image bullets so they would have been stripped out upon export to Excel. Excel also does not support some other features (checkboxes for instance), some functions, and some formatting. Luckily your spreadsheet had no problems in the conversion to and from Excel.

My first thought was maybe you opened an Excel spreadsheet in Numbers. Sometime you get messages similar to that.

SG