So I tried the requests, and I think it has more to do with a data issue with one of the groups in the result set.
We'll need to look into which group is causing this; however, if you increment the startIndex past 300 it seems to work fine.
Also, it is recommended since Groups can often be quite verbose in their payloads (same with content for that matter), it is best to be explicit with what fields you need and do not need (i.e. -resources,-creator.resources, etc.)
Hope that helps.