Alert Tsunami: Why the Huge Delay and Flood of Post-Resolution Power Alerts?

Have you verified your org's email filter isn't the culprit? If there is a tsunami of alerts coming in, an email filter might start blocking all emails from a sender for additional sandboxing. You can verify the true sent time in the email headers. Whitelisting LM emails might fix this. If you're not allowed to whitelist LogicMonitor with your email filter, you could also look cluster alerting and disabling individual alert notifications.
https://www.logicmonitor.com/support/cluster-alerts#h-managing-cluster-alerts