I collectes all of the resonance gems from across Solstheim, but the Reaver Lord inside of the Kagrumez ruins did not spawn. So I now have 3 of these gems, but cannot continue because I'm one gem short. Advice?

i am having this issue as well.. i think the problem may be that u can not ever go into Kagrumez untill u have found all 3 gems then u go in ..if u go in before u bug it out. im having the isssue where i have 2 of the gems but im missing the 3rd from Nachardak and i cant get back in ;(

I collected the other three gems beforehand and when I entered for the first time, there were no problems. I'm not sure if this is related, but it might be worth a shot to try. Good luck!

wait 30 days outside of the ruin then go in. If not there head to the other dungeons as for me the ones there have respawned. I currently have 8 or so gems