"There was an error processing your request" when submitting build for External Beta App Review

Getting this error trying to submit a build for External Beta App Review:

"There was an error processing your request. Please try again later."

Build shows "Ready to Submit," internal testing works fine, error happens even before selecting a build. Retried several times over a few days, no change. Checked export compliance, still confirming Test Information is fully filled out. Anyone hit this exact error, especially at the build-selection step?

"There was an error processing your request" when submitting build for External Beta App Review
 
 
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