Heads up — there might be a bug in STM 1.12.3 (Unity 2021.3.4) that causes events to be missed after calling Rebuild. Try subscribing to OnCustomEvent and testing it with something like this:

void OnCustomEvent(string eventTag, STMTextInfo info)
{
    Debug.Log("Executing event '" + eventTag + "'\nFrame " + Time.frameCount, gameObject);
    StartCoroutine(PauseReading());
}
IEnumerator PauseReading()
{
    stm.Rebuild(stm.currentReadTime, readAutomatically: false, executeEvents: true);
    yield return new WaitForSeconds(1f);
    stm.Rebuild(stm.currentReadTime, readAutomatically: true, executeEvents: true);        
}

And you can use string like this:

This is a test string<e=event1> with multiple events<e=event2>, but the subsequent events won't fire<e=event3> if we rebuild the mesh.

When I tried this in a fresh project, only event1 was fired.

In this particular case, I think I was able to work around it by just using <pause> and Continue() like you're supposed to. But I did run into some weird edge cases where Rebuild was messing things up (actually, I think my mesh was rebuilding because the bounds was changing when the line finished reading out, and that's what caused Continue() to not work when I first tried it).

Ah yeah in this situation, I'm going to say stick to using <pause> and Continue(), or use the delay tag. (<d=10>) to delay by 10 imaginary characters being read out. I'm curious what happens if your custom event calls stm.Pause() and then stm.Continue instead, though? Either way, I think the delay tag might be better suited  for this situation!

Wait, where is stm.Pause() located? I see a pauseCount and a currentPauseCount, but I don't have a method called Pause().