seems like GatewayManager 1.1.1pl is the problem. i figured out that it is just listing one resource from web1 context under "startpage". all other resources are listed there are from web context. the other resources from web1, created after GatewayManager installation, are missing.
i did set the startpage accidently to a resource of the default web context. then i could access all the other resources in the context web1.
just the startpage brought a 404 in the title -> 503 page not found on the page.
I removed the GatewayManager and switched to ContextRouter. It is a bit more configuring but it is runing fine now.