Coroutine stops after any yield statement halfway through

Hi - I have a coroutine that calls several other coroutines in sequence. So far I have been quite successful at using nested coroutines to sequence certain animations, etc., but this particular one has been causing me trouble for a while. The (simplified) coroutine is as follows:

 public IEnumerator UnitDeploy(UnitCardView deployed, UnitView target) 
 {
         // Multiple yield returns before this which function fine
         UnitView deployView = RowView.DeployedUnit; 
         RowView.DeployedUnit = null;
         Debug.Log($"{deployView} {deployView.MyUnit}"); 
         // prints a non-null MonoBehaviour class name for deployView
 
         if (target == null) {
             Debug.Log("Starting playdeploy coroutine"); // prints this
             yield return deployView.PlayDeploy();
             Debug.Log("Started deploy animation"); // does not print this
             deployCard.ActionPrimary(null);
         } else {
             Debug.Log("Has target - playing secondary cast"); // prints this
             deployCard.ActionPrimary(target.MyUnit);
             StartCoroutine(deployView.PlayCast(true));
             yield return deployView.AnimateSecondary(target, deployCard);
             Debug.Log("Done playing deploy secondary animation"); // does not print this
        }
 }

PlayDeploy() and AnimateSecondary() are both coroutines to which I've added a Debug.Log as the final line - this line also always prints. I don't understand how it's possible that the last line of the called coroutine executes but not the next one in the caller? yield return AnimateSecondary() is called from other coroutines in this file and works fine, so I'm pretty sure the issue is somewhere in this method...

Adding the PlayCast() code as requested... but this, too, is called from other places and works fine from there.

 public virtual IEnumerator PlayCast(bool secondary) {
             GameObject muzzlePrefab = ... // gets a file from Resources
             AudioClip muzzleSound = ... // gets a file from Resources
     
             yield return PlayVFX(muzzlePrefab, muzzleSound); // plays these files - executes correctly
 }