Vaal Tempel

I have the problem that I can see dropped medallions on the minimap, but they aren’t shown in the game world. I simply can’t pick them up.
I also can’t start the boss that drops the Core Destabilizer because I can’t click on the Soul Core.
Can anyone help me with this?

Did you leave the instance somehow and go back in? Like, logging out and back in, or something similar? I had something like this happen once, when something wonky happened with my instance and I could keep doing the temple but I couldn't interact with anything in it. It happened before the most recent patch (0.4.0e) and I don't know if the newest patch changed anything in that regard, but it's worth mentioning.

I'm not even sure what I did; I think I left via the Waypoint to disenchant stuff (Doryani why please just disenchant things for me my guy), then when I tried to go back via the Waypoint I was in a different instance. So I went back to the map I originally accessed the temple from, it said it was "closed" on the instance manager but I could still get in for some reason? And I was able to get back into the temple from there.
It was weird, I don't really understand so I can't really explain it.