When one mirror is slow

A mirror can be slow and still be fine. Slowness usually means the circuit is taking longer to build, often because the network is busy, and the store behind it is exactly as available as the others. A dead mirror is different. It gives no response at all after a few patient minutes.

The practical move is the same either way. Do not fight the one that is struggling. Switch to another address from the list and let that one build its own path. Because all three open the same storefront, you lose nothing by changing doors, and the switch takes a few seconds.

Keep two or three mirrors saved rather than one. That is the whole habit. A single saved address is a single point of failure, and a small set of them turns a bad day into a non-event.