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If you would like to continue to use automatic sending for split test marketing tools campaigns at the campaign level, the account setting should be enabled/ checked. With that setting enabled different win criteria can be selected for automatic sending at the campaign level and it ensures the winner will be selected and sent.
Temporarily rely on manual sending. At the Sending stage for split test marketing tools campaigns, select The winner will be chosen option.
🕙 Timeline: The issue is currently being reviewed Solutions are being investigated by our developers for possible solutions. After a solution is determined a more specific timeline will be provided to clients. The issue is tentatively expected to resolved in the October 4th release.