A cloud-based service included in Microsoft 365, delivering scalable messaging and collaboration features with simplified management and automatic updates.
The Out Of Office auto reply only fires once per sender and there is no way to change that. So the same sender can sender multiple messages, but they will only get one reply while its enabled. Disabling and re-enabling it will clear those entries and start fresh.
https://learn.microsoft.com/en-us/exchange/troubleshoot/client-connectivity/one-reply-sent-sender