Hi!
I use OsmAnd~ version 3.9.6 because, on my phone, I find that newer versions take longer to calculate routes or even fail to do so, when the version I use does it and quite quickly.

I'm relaying this because I wonder if the version could have anything to do with this issue.

Even when creating routes further east and west, that would end up routing through this area, it tends to calculate longer routes, seemingly to avoid passing through here.

Ex.: From 'Avenida Marginal, Monte Estoril' to 'Avenida Nossa Senhora do Cabo'/'Farol da Guia', it calculates a less direct route close to the sea port down south:
https://i.imgur.com/vmfBjj3.png

If I set OsmAnd~ to "Avoid Road" on the 'Avenida Dom Pedro I' it still calculates a really weird route seemingly to avoid that area.

The Avoid Road placement: 
https://i.imgur.com/qknPBBT.png

The new route:
https://i.imgur.com/p9HDU5j.png

"We could go and ask on the OsmAnd forum about this"

Sure, I'd be interested in knowing what's going on over here as well, at least to know whether I need an updated OsmAnd.

Do you mind doing it and dropping the link to it here?

And thank you for your work!