You may see something like this when you go to Manage Products on a product group.
This means that you have some other process going on that is updating or creating products like:
Running a CSV import to your product catalog
Using an app that goes through and make updates or adjustments to products
Using an app that is adding new products to your shop in bulk
When there is some bulk process happening on your products catalog from outside the app, the product sync is trying to play catch-up with all those updates.
So you should wait until that product updating/process is completed, and then when the 'waters are still' go into the app again and re-attempt to manage products.
If you have a large catalog, it make take a little while for the app to sync the updates and changes.