This started happening a while back, maybe around 2.3, after a fairly major update, but I used to have sraidframes setup to show warlock castable buffs, and this included SS. At some point, an update was released to the addon, and I can no longer get SS to show up.
I have it set to show buffs castable by me and my class, and I can see just fine when I cast see invis or water breathing on someone. But I can no longer see who has soulstone. I even added it to the "always show these buffs" list ("Soulstone Resurrection"), and that didn't help.
Anyone have ideas? It was very convenient to see who had SS.
I've experienced the same thing occuring with sRaidFrames and the soulstone indicators. I tried the same work around pox_x described with no luck either. Hope this functionality can be fix since I rely on sRaidFrames to know who has a soulstone.