Hi @philhosophy 
This is to be expected. It is also mentioned in the OpenAI docs.
The API is stochastic by default which means that you might get a slightly different completion every time you call it, even if your prompt stays the same. You can control this behavior with the temperature setting.
I’m not 100% sure on how to fix this but, being very intentional/specific with the prompt and providing examples of how you want it to complete may help.
e.g If you want a detailed completion, you can make the prompt as:
Describe the link between (1) and (2) in detail
or
Describe the link between (1) and (2) in 30-40 words.
Hope it helps.