You could try restarting your browser or using an incognito tab. 220 isn't that many images. How many images were you attempting to upload?
Do other browsers do this?
When the uploader is analyzing your tags it can take up a bit of memory. The resolution downscaling setting does not affect this since the downscaling is done on the server. The internet connection shouldn't matter either. It sounds like the issue was happening after the upload of the files was already started. At that point all of the analysis has already been done.
The classic workflow doesn't do this analysis so requires less resources.