Comments don't load/take a while to load sometimes because the architecture is still laggy and servers take time to talk to each other and sync information - this is one of Lemmy's biggest sticking points so far, but it comes with the territory of having multiple decentralized servers constantly exchanging info between them.

It'll be particularly egregious for a while because of the huge influx of people but eventually, with a bunch of stability updates and centralization for the important stuff, the experience should pick up in due time, hopefully.