Zephyr Squad slow to load tests

Hi, we're using Zephyr squad to test a new piece of software and it can take 10-20 minutes to load some of the tests. It's very frustrating for users to use. It's intermittent. Sometimes it loads quickly, sometimes not. 

We've rebuilt indexes and cleared caches. It's still a recurring issue over the last 6 months.

What would be causing this issue? 

Ross