I have The Ritual stone on my character, and I know all descriptions of the stone are that it will summon numerous corpses around you to fight for you.

However, I was just doing a quest in Markarth - the one where you kill off the big spider in the excavation site - and I tried to use the Ritual Stone power in the dungeon area. There were 2 Frostbite Spider corpses when I used the power, but one one of the spiders was resurrected. They were right next to each other, and right in front of me, there's no reason why distance should have been an issue.

Also, while I wasn't paying enough attention at the time, I was also in a barrow (the one in the Ivarsgread limits), in a room full of Draugr, when a Draugr boss spawned, so I used the Ritual Stone power in the room, and I feel like afterwards, I still saw a bunch of corpses laying on the ground, and I don't particularly recall seeing a bunch of reanimated Draugr coming to my aid.

Are there any issues with this power that I'm unaware of? Is there something I'm doing wrong in using it?

I think it only works on humanoids.

You have to aim it at the corpse you want to thrall too.

I know in a previous play through, I had reanimated 2 Frostbite Spiders - although it was in a different dungeon.

I don't recall if I ever specifically aimed at any corpses though. Especially since it raises numerous ones, it'd be real difficult to aim at 2 or more corpses at once.

Huh... I don't know what to say then. I've only used it on humanoids, and I figured it worked a lot like Dead Thrall, only with a timer.

In my experience it seemed like you had to aim it for it to work.

According to UESP, it affects everyone behind you, and it affects creatures and humans. In fact, it's the only way to resurrect giants and mammoths

Must be a bug as I've used it on most mobs in Skyrim with no problems. Perhaps switching to another stone and back again could resolve the issue (worth a try, at least).