By default, Sprout Studio uploads 4 images at a time, and has an automatic time out after 45 seconds if an upload doesn't finish. If you have a slower internet connection and larger files, it could attribute to your uploads failing.
Go to Settings > Account > Users > Your Profile to change your upload speed in the "Gallery Upload Mode" section. If you find that you have errors during upload, it's usually an indication of the upload trying to go faster than your internet will allow for. Try choosing the speed setting below the one you're currently set to and you should see fewer errors.
When uploading photos, there are three speeds at which you can upload:
Slow, which is the option you should use if you have an intermittent or slow internet connection.
Normal, which is the option you will most likely be using.
Ultra, which is only to be used if you have a very fast internet connection.
Should I resize my photos before uploading them?
Resizing your photos before uploading them will speed up the upload and not count as much towards your storage/usage count. If you plan on offering digital downloads and would like to offer a high-resolution download, we recommend resizing your photos to 5000px wide before uploading them. If you are not planning on offering digital downloads, we recommend resizing your photos to 2400px wide before uploading them.