Castle not firing??

Hey all,

So I just played a game where I dropped a forward castle. As you can see from the photo, I ran out of units to support the castle lol, but I was still hoping the castle could do some damage. I understand that a castle cannot fire at its base until murder holes is researched, but my castle oddly sat idle for long periods of time without firing at anything. The screenshot I included was during one of these dead periods, it wasn't trying to hit anything even though there were several units and buildings within range and not at the base. Then it would randomly fire at a unit for a short time before it went into the base of the castle, and then stop firing arrows again.

Does anyone know why this happens sometimes? It's not the first time I've had a stubborn castle that doesn't seem to want to put in work. Or is this a bug?

Thanks in advance!