Hard 0FPS Lag Spikes and Looking For Clues in the Tour Shard

[PeaTeaSix]

Light spoilers below so stop reading if you're still going through the game. I tried to be vague enough not to ruin anything major, but needed to be descriptive enough to talk about what's happening.

I haven't tried a PC restart yet, which is coming right after I post this, but I figured I'd ask here to see if anyone is experiencing the same. Can't tell if it's because my save has over 100 hours of playtime on it, or if it was the 2.5 patch or what. My game ran flawlessly up to Act 3. I was cleaning up the last of my side missions, and when I was working on the wild goose chase for Nancy's story (trying to be vague but still hint at what mission), it's like the game ate ♥♥♥♥. Every few minutes, frames drop to 0, game locks for about a half a second, before picking back up to 120+ FPS. Should I push to beat the game before the save file dies entirely, or is this a patch issue that I need to find a workaround for?

Secondly, I cannot finish one of my missions. In the mission where you do the tour of NC, there is an encrypted shard that I have to look at for clues. I have opened and scanned this shard several times, but nothing seems to pop the trigger for the next step of the mission. I'm just forever stuck "Looking for Clues in the Tour Shard." Anyone else find a fix for this?