here's the log from debug after changing value in hostgroup selector
2018-09-14T11:42:34 [I|app|] Started POST "/hosts/process_hostgroup" for ::1 at 2018-09-14 11:42:34 +0200
2018-09-14T11:42:34 [I|app|7bf88] Processing by HostsController#process_hostgroup as */*
2018-09-14T11:42:34 [I|app|7bf88] Parameters: {"utf8"=>"✓", "authenticity_token"=>"DDCHnB+lFIL27WbTJObgYT9H0IviSBxA45F/Hx9pas7ZwOJdyjdEzspQcw2aZ9jNxlMSaQSL2KRQUCdJV5m0Bw==", "host"=>{"name"=>"mac52e84c4b71d7", "organization_id"=>"3", "location_id"=>"2", "hostgroup_id"=>"5", "environment_id"=>"", "puppet_proxy_id"=>"", "puppet_ca_proxy_id"=>"", "managed"=>"true", "progress_report_id"=>"[FILTERED]", "type"=>"Host::Managed", "interfaces_attributes"=>{"0"=>{"_destroy"=>"0", "mac"=>"", "identifier"=>"", "name"=>"mac52e84c4b71d7", "domain_id"=>"", "subnet_id"=>"", "ip"=>"", "ip6"=>"", "managed"=>"1", "primary"=>"1", "provision"=>"1", "tag"=>"", "attached_to"=>"", "id"=>"3363"}}, "architecture_id"=>"", "operatingsystem_id"=>"", "build"=>"1", "medium_id"=>"", "ptable_id"=>"", "disk"=>"", "is_owned_by"=>"3-Users", "enabled"=>"1", "model_id"=>"", "comment"=>"", "overwrite"=>"false", "id"=>"2357"}, "fakepassword"=>"[FILTERED]"}
2018-09-14T11:42:34 [D|sql|7bf88] User Load (0.4ms) SELECT "users".* FROM "users" WHERE "users"."id" = $1 LIMIT $2 [["id", 3], ["LIMIT", 1]]
2018-09-14T11:42:34 [D|sql|7bf88] AuthSource Load (0.4ms) SELECT "auth_sources".* FROM "auth_sources" WHERE "auth_sources"."id" = $1 LIMIT $2 [["id", 1], ["LIMIT", 1]]
2018-09-14T11:42:34 [I|app|7bf88] Current user set to admin (admin)
2018-09-14T11:42:34 [D|app|7bf88] Current location set to none
2018-09-14T11:42:34 [D|app|7bf88] Current organization set to none
2018-09-14T11:42:34 [D|sql|7bf88] (0.2ms) SELECT "taxonomies"."id" FROM "taxonomies" WHERE "taxonomies"."type" IN ('Location') LIMIT $1 [["LIMIT", 1]]
2018-09-14T11:42:34 [D|sql|7bf88] (0.2ms) SELECT "taxonomies"."id" FROM "taxonomies" WHERE "taxonomies"."type" IN ('Organization') LIMIT $1 [["LIMIT", 1]]
2018-09-14T11:42:34 [D|sql|7bf88] Organization Load (0.3ms) SELECT "taxonomies".* FROM "taxonomies" WHERE "taxonomies"."type" IN ('Organization') AND "taxonomies"."id" = $1 ORDER BY "taxonomies"."title" ASC LIMIT $2 [["id", 3], ["LIMIT", 1]]
2018-09-14T11:42:34 [D|sql|7bf88] Location Load (0.2ms) SELECT "taxonomies".* FROM "taxonomies" WHERE "taxonomies"."type" IN ('Location') AND "taxonomies"."id" = $1 ORDER BY "taxonomies"."title" ASC LIMIT $2 [["id", 2], ["LIMIT", 1]]
2018-09-14T11:42:34 [D|sql|7bf88] Hostgroup Load (0.3ms) SELECT "hostgroups".* FROM "hostgroups" WHERE "hostgroups"."id" = $1 ORDER BY hostgroups.title LIMIT $2 [["id", 5], ["LIMIT", 1]]
2018-09-14T11:42:34 [D|sql|7bf88] Host::Base Load (0.3ms) SELECT "hosts".* FROM "hosts" WHERE "hosts"."id" IS NULL LIMIT $1 [["LIMIT", 1]]
2018-09-14T11:42:34 [D|sql|7bf88] Hostgroup Load (0.3ms) SELECT "hostgroups".* FROM "hostgroups" WHERE "hostgroups"."title" = $1 ORDER BY hostgroups.title LIMIT $2 [["title", "5"], ["LIMIT", 1]]
2018-09-14T11:42:34 [D|sql|7bf88] CACHE Hostgroup Load (0.0ms) SELECT "hostgroups".* FROM "hostgroups" WHERE "hostgroups"."id" = $1 ORDER BY hostgroups.title LIMIT $2 [["id", 5], ["LIMIT", 1]]
2018-09-14T11:42:34 [D|sql|7bf88] Hostgroup Load (0.4ms) SELECT "hostgroups".* FROM "hostgroups" WHERE "hostgroups"."id" IN (1) AND (compute_profile_id is not NULL) ORDER BY coalesce("hostgroups"."ancestry", '')
2018-09-14T11:42:34 [D|sql|7bf88] Hostgroup Load (0.3ms) SELECT "hostgroups".* FROM "hostgroups" WHERE "hostgroups"."id" IN (1) AND (realm_id is not NULL) ORDER BY coalesce("hostgroups"."ancestry", '')
2018-09-14T11:42:34 [D|sql|7bf88] Hostgroup Load (0.4ms) SELECT "hostgroups".* FROM "hostgroups" WHERE "hostgroups"."id" IN (1) AND (compute_resource_id is not NULL) ORDER BY coalesce("hostgroups"."ancestry", '')
2018-09-14T11:42:34 [D|sql|7bf88] User Load (0.4ms) SELECT "users".* FROM "users" WHERE "users"."id" = $1 ORDER BY firstname LIMIT $2 [["id", 3], ["LIMIT", 1]]
2018-09-14T11:42:34 [D|app|7bf88] not found: Couldn't find Nic::Base with ID=3363 for Host::Managed with ID=
2018-09-14T11:42:34 [I|app|7bf88] Rendering common/404.html.erb within layouts/application
2018-09-14T11:42:34 [I|app|7bf88] Rendered common/404.html.erb within layouts/application (0.7ms)
2018-09-14T11:42:34 [I|app|7bf88] Rendered layouts/_application_content.html.erb (0.5ms)
2018-09-14T11:42:34 [I|app|7bf88] Rendering layouts/base.html.erb
2018-09-14T11:42:35 [I|app|7bf88] Rendered layouts/base.html.erb (131.1ms)
2018-09-14T11:42:35 [I|app|7bf88] Completed 404 Not Found in 159ms (Views: 134.6ms | ActiveRecord: 3.9ms)