A common issue we have seen people run into is the limit that Shopify imposes on the number of variants (SKU's) that can be uploaded per day.
A Shopify store can only upload 1000 variants per day. This limit does not apply to Shopify Plus stores. You can find more information from Shopify here.
To reduce the chance of crossing the threshold, we recommend limiting the number of colors and sizes when creating multiple products per day.