My team often finds that opening a task run in the UI takes around 5 minutes, which often makes us prefer to kill the whole flow and restart instead of manage the tasks individually. Is there a reason this might be the case?

No, not at all. 1. Are you on Cloud or Server? Can you share your output of “prefect diagnostics”? 2. If you’re on cloud, can you share your team slug via DM? 3. Which browser do you use? Did you try refreshing your browser and clearing browsing history? 4. Does it happen only for a specific large task run or for all task runs across all flows?