Why would alerts still get sent out when node is muted?

Being the Solarwinds SME at my work, I sometimes have to explain things to others in IT. Today, I explained that we can stop alerts of a node we still want to collect data on by muting the alert. As opposed to Unmanaging the alert, which stops both alerts and data collection. Having explained that, I then muted 4 devices which have been consistently alerting to show them how it was done. All fine and dandy until several hours later, new alert e-mails on the same nodes show up in my inbox. I immediately jumped into Manage Nodes and ran a search for the nodes. They show up as still muted! Could anyone suggest why we might still get alerts on nodes that are muted?

Additional info:

The alert is on Volume (as opposed to alerting on Interface or Node) status.

Scope of Alert: All objects in my environment

The triggers are:

Volume Percent Used is greater or equal to 90%

Volume Capacity_Class is equal to 90

The Volumes are on servers. While I do have SAM installed, I think this alert just replies on NPM information.

Here are our versions: Orion Platform 2018.2 HF3, VNQM 4.5.0, NCM 7.8, NPM 12.3, NTA 4.4.0, SAM 6.6.1, Toolset 11.0.6

Running on Windows 2016, SQL 2016

The only thing I can think of is that someone edited the alert, which kicked off new alert e-mails when the changes were saved. But shouldn't those emails be squelched by the mute setting? Or maybe someone could have unmuted, and then remuted before I logged in and saw that. I checked the system events. WHile the events has a search for managed node and unmanaged node, there is none such for muted and unmuted.

Thanks, Eric

ps. If you point out this is not the most effective way to do an alert, I would agree. The creator of these alerts has 8 alerts set up, one for each of 8 different thresholds. Were I to have set this up, I would have used this as a trigger, and just one alert for all thresholds: Volume Percent Used is greater or equal to Capacity_Class