You can probably make the sound loop through GScript and the finished
signal. Something like this:
extends AudioStreamPlayer
export (bool) var loop_sound = true
func _ready():
connect("finished", this, "_on_finished")
func _on_finished():
if loop_sound == true:
play();
Then you can trigger it to start playing like a normal AudioStreamPlayer. Though, having the loop option selected should make the audio loop. Maybe its a bug? If there is not one already open on this issue, it might not be a bad idea to open a bug report on the Godot GitHub (I didn't see any issues on the topic, but I only took a brief look). If you can, a minimum replication project that shows the bug would also be so developers can see if the bug is fixed, but is not required.