When you conjure a block far enough away from you, it can take a couple seconds for the particles to render. This is a simple spell that conjures a block 20 meters in front of you. It can take several seconds to show up. Using distances larger than 20, sometimes the particles never show up until you get closer.

This is intended behaviour, minecraft has a 13 block limit on particles.
So if you're more than 13 blocks away from the conjured block it won't render its particles.