So I've seen others post similar problems but most responses are fairly old. Right now I am simply trying to fill up a cup, however, the cup only gets filled with particles a quarter of the way and does not raise any higher. I have done several things such as, increase substeps, make thicker geometry, add a divergence field (made liquid in glass raise but added a weird pumping effect that did not look good at all), and even messed with scaling but I have had no luck. Does anybody have any suggestions, I'm stumped.

Volume loss is usually happening because of the grid size not being able to resolve everything. Try lowering it to 1. I would then try to find the biggest number that still gives the desired result, as this setting can have a huge performance impact.
You also need to play around with particle separation, particle size and double check your collision geo, but usually this is connected to the grid size.