Cognito UserPool behave differently in me-south-1 and us-east-1

I'm having an issue trying to login to perform authorization code grant with swagger-ui against cognito in Bahrain. My "setup" used to be working fine for months, but today it's not (no changes were made on my side). For comparison I've created identical user pool in us-east-1 and swagger-ui is able to perform login with no issue with new pool. Details about error I observe: swagger-ui on it's "redirect" endpoint uses "window.opener" to complete code exchange. On redirect from me-south-1 user pool "window.opener" is null, so swagger-ui isn't able to complete code exchange. According to docs one possible reason for "opener" to be null is having a Cross-Origin-Opener-Policy header with a value of "same-origin", that's what I assume is the reason.