Add more debug logs to understand if statement-distribution misbehaving (#3419)

Add more debug logs to understand if statement-distribution is in a bad
state, should be useful for debugging
https://github.com/paritytech/polkadot-sdk/issues/3314 on production
networks.

Additionally, increase the number of parallel requests should make,
since I notice that requests take around 100ms on kusama, and the 5
parallel request was picked mostly random, no reason why we can do more
than that.

---------

Signed-off-by: Alexandru Gheorghe <alexandru.gheorghe@parity.io>
Co-authored-by: ordian <write@reusable.software>