After upgrading to 2.11.0 (from 2.10.0) I am no longer able to submit seed requests for tiled layers in the web UI. I get the error message:
Unknown or malformed request. Please try again, somtimes the form is not properly received. This frequently happens on the first POST after a restart. The POST was to /geoserver/gwc/rest/seed/imagery
However, I've noticed that seed requests sent from one of my automated scripts still works just fine.