Have you modified the default unbound config at all? This sounds like increasing the cache size limits and timeframes in the unbound config could help.

I’m actually chasing an issue I’ve always had where everything works great in my environment, but on mobile certain domains take ages to finally load up for me. I think it’s a combination of my Pihole blocking and the amount of domains tied to a page (advertisements and tracking), but would love to figure it out. I work around it right now by flipping wifi off and on again in those instances.