I've got a very slow login page with Hotspot.
Is there a cache fix or?

I have 5 AP's connected to Box with RouterOS4.11. via bridged backhaul.
Once login page loads, everything is fine.

All unauthenticated users are going to fall into the queue dynamically created based on the rate-limit values that are set on the Hotspot server profile. If that is set to a very low speed a resource intensive page would load slowly.

All unauthenticated users are going to fall into the queue dynamically created based on the rate-limit values that are set on the Hotspot server profile. If that is set to a very low speed a resource intensive page would load slowly.

Are you saying the "Rate Limit (rx/tx)" drop down on the Hotspot Server Profile page in Winbox is the rate limit for unauthenticated users -each?
I was under the assumption it was the rate limit for the entire hotspot.

You're correct, and that's what I meant. The rate limit on a Hotspot server profile generated a dynamic simple queue with the specified rx and tx values for dst-address 0.0.0.0/0, the interface the Hotspot is on, and a direction of 'both'. All unauthenticated users share that queue. If you have a bunch of people loading a login page and the rate limit on the Hotspot server profile is set to something low like 128k/128k the pages are going to load extremely slowly.
Users that are logged in and authenticated are served by dynamic simple queues higher up in the list (so they hit first) specific to their IP address, and do not fall through to the shared pool.