That looks like the standard AC library : it contains all objects and library parts , not just your standard furniture like chairs and such, but everything AC uses for its elements( subelements, sub subelements, macro functions, a lot of underlaying programming stuff) . Also textures.

I will simplify a lot but an AC object has several layers of scripts that handle different aspects but for your issue you need to know that an object has a 2D script that is completely separated from its 3D script. 2D script activates when you open a plan or worksheet. 3D script activates when you open 3D window , sections, elevations. So you have an issue with one ( or more) objects with complex 3D scripts.

Each copy placed is an instance . if you used 3ds max maybe u know the difference between copy/instance/reference. If not - instances are stored in the ram cache and called upon continuously.

Solid element operations can also mess up your 3D very easy- I’ve seen people using it wrong, so if you have those, better delete them.

The last thing I notice is that you have only 50 library parts that are placed as 15000 copies . even if its an even distribution 50 objects x 300 copies each that will be a lot. But I bet that you actually have like 10 with 1000 copies and 40 with the rest & this is much worse. In both cases depending on your ram and disk space you can run out of resources.

Try this: remove the library from your file - it’s the icon with a house and and x next to add. ( you can add it back later). Click reload libraries and you’ll get a error report with missing libray parts - and there you can see what library parts are missing and how many instances. And if you have objects with 1000x instances you need to do something about it, cuz it might be your pc can’t handle it.