Hi,
Looks like a problem with generator=prefixsearch queries. Properties always missing for the last item (20th page in the examples below) in the returned results. 
I don’t see this issue for generator=geosearch.

Here are the examples:

https://en.wikipedia.org/w/api.php?redirects=1&exintro&gpssearch=New&gpslimit=20&inprop=url&explaintext&action=query&prop=extracts&exsectionformat=plain&exlimit=20&continue&exchars=150&generator=prefixsearch
https://en.wikipedia.org/w/api.php?redirects=1&gpssearch=New&pithumbsize=100&gpslimit=20&action=query&pilimit=20&prop=pageimages&continue&generator=prefixsearch


Thank you.