Bad performance for graph api

Question

The bug:
When using MS Graph API to scrape users and groups deltas and there's a lot of data to fetch, each response (containing the deltaLink) contains much less than the max 1000 entries.
For users request we get fixed size of 200 entries per response.
For groups request we get varying number of entries in the response, starting from about 200, and decreases each time until it gets to 1 entry in each response. After quite a few of such 1 entry responses it gets back to around 200 entries per result, and continues decreasing in next responses.
We see the same behaviour when using the Azure portal as well.
We experience this problem with few different tenants of our customers.

Steps to reproduce the behaviour:
Use 'https://graph.microsoft.com/v1.0/xxx/users/delta' or 'https://graph.microsoft.com/v1.0/xxx/Groups/delta' when there are a lot of users and groups. Use the url in the deltaLink in the result for your next request, and check how many entries are in the 'data' field.