Hi everyone! 
Quite some time ago (February) we identified an issue with the seasonal closures: https://forum.myrouteapp.com/topic/3343/here-issue-regarding-seasonal-closures
Unfortunately the issue affected a lot of routes, created by many users over quite a long time
We were (and still are) very sorry for the inconvenience this caused. As stated in the forum post above, it however wasn't an issue from our side.
Today I've received confirmation from HERE that we are able to use a temporary workaround while their internal development team starts working on a more permanent solution (finally).
As of now, the website is updated to use the temporary workaround! 
If we take the following mountain pass as example, you would always be routed the long way around the mountain. Regardless of your seasonal closure setting

If you turn off the seasonal closures using the toolkit, the route now does what you expect! 

I'm happy with the solution we now have and once again, sorry for the inconvenience.
Best,
Team MRA 