Various errors (502, 403) occurring with no pattern

You have 30 API keys!
First off, if you breach our fair use policy, you will be immediately (without notice) and permanently denied access to our services.
Aswell as the API rate limit checking, there is also IP limit checking. If you exceed this you will be banned.
If you are banned you will get 403.
If you are rate limited you will get 429.