Shadow issue in EEVEE

Here is a screen capture of the issue I’m having.

As you can see, the shadow being cast by the smaller sphere is perfectly normal, until it starts to approach the edge/more vertical slanting side of the larger sphere, and it becomes all jagged and rough. Why is this? Is there a solution, or is this just one of the downsides of realtime rendering?

What do you mean?

To start with, I’d take a close look at the geometry there. Are there, for example, doubled-up planes? It looks to me like there’s some kind of ragged edge there …

Nope. It’s just the default sphere. I’ve also found a similar issue here