Error message: Photos has stopped responding

I have been using iCloud.com to upload photos to my iCloud photo library. After uploading some 3800 pics, I am getting a persistent error message when I try to open the Photos tab on iCloud.com.

Tried to append a screenshot but this comment box won't accept the .tiff format images produced by the Grab app. The message says:

"Photos has stopped responding.

An error has prevented this application from working properly. Help Apple improve its products by sending us diagnostic and usage information about iCloud."

Then there is an option to Reload which just repeats the error, or Send to Apple, which presumably sends a message, then repeats the error.

Any ideas how to resolve this?