Strange navigation - Waze tries not to route fastest way.

[Instigater]

Waze constantly tries to avoid fastest highway. Checked every segment, no restrictions, no lower class than highway. What could be the problem?

The purple road on first pic and the blue road on second pic are fastest from coastal part of Latvia to Daugavpils.


And here are all not so optimal routes. As soon as starting point is at the coast or further to the left, the optimal route is forgotten.