Internet was probably not good (edge in the screenshot) but than, BRouter should have jumped in.
When I put my phone into airplane mode BRouter does work.
If there was not internet and BRouter activated,
you had downloaded the BRouter data for the area?
Network detection on Android is problematic.
As agreed with users, selecting Kurviger / BRouter in settings,
Kurviger tries to recalculate a route if there is internet,
and in case of failure, the next rerouting is done with BRouter.
If there is no internet, BRouter is used immediately.
You can check again with the next app update that will have rerouting improvements:
(especially with BRouter offline rerouting)