This problem happens to me sometimes too. It used to happen more in older code versions like early 18.3 code and I have not seen it lately on 18.4 or 20.1 Viptela OS. Whenever I saw it, I just kept retrying until it didn't error out and eventually it worked. If you see it consistently, try a different browser or a private browser and see if that helps. If you still cannot get it working, I would recommend opening a TAC case.
Hope it helps,
Steve
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