SharePoint Search API result returns unexpected RowCount

Hi

I am struggling to understand why the following request

https://%xyz%.sharepoint.com/_api/search/query?querytext='marco'&rowsperpage=10&rowlimit=200&clienttype='ContentSearchRegular'

Results in a row count of 2 whereas 

https://%xyz%.sharepoint.com/_api/search/query?querytext='marco'&startrow=1&rowsperpage=10&rowlimit=200&clienttype='ContentSearchRegular'

Results in the expected row count of 10

Initially the first query worked fine (since 2017) and the unexpected result is new. Therefore I believe it may be related to an update by Microsoft. Curious to see if anyone else is experiencing the same thing!

PS What is also odd is that for other queries e.g. 'sharepoint' I get immediately 10 rows of results.