If trigger execute is called in Blueprint, it will fire every time the sound recovers from being virtual, even if it has not been called again.
See video example:
Also occurs in Release 5.2
1) In the Content Browser, create a MetaSound Source asset and open it.
2) Remove the One Shot Interface
3) Add an Input of type Trigger and set it to do something (play a sound, print a log, etc)
4) Add an Attenuation to the MetaSound and ensure that Virtualization Mode is set to Reset
5) In a Blueprint actor or the level blueprint, set the MetaSound to play on level start
6) Use a trigger box or key press to call Execute Trigger Parameter on your trigger
8) Let the sound become active and fire the trigger
9) Exit and Enter the attenuation field so that the sound becomes virtual and then not
The trigger call is a fire and forget
The trigger is executed every time the MetaSound restarts, even through it was only fired once
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-194378 in the post.