Fixed

app/controllers/semester_process_volunteers_controller.rb

@@ -40,7 +40,7 @@ class SemesterProcessVolunteersController < ApplicationController
     authorize SemesterProcessVolunteer
     semester = Semester.parse(params[:semester])
     @semester_process = SemesterProcess.find_by_semester(semester).last
-    @q = SemesterProcessVolunteer.index(semester).ransack(params[:q])
+    @q = SemesterProcessVolunteer.index(@semester_process).ransack(params[:q])
     @q.sorts = ['volunteer_contact_last_name asc'] if @q.sorts.empty?
     @spvs = @q.result.paginate(page: params[:page])
     set_responsibles

app/models/semester_process_volunteer.rb

@@ -33,12 +33,14 @@ class SemesterProcessVolunteer < ApplicationRecord
   validates_associated :hours, :semester_feedbacks, :volunteer
 
   scope :index_joins, lambda {
-    joins(:semester_process).joins(volunteer: [:contact]).joins(:semester_process_volunteer_missions)
+    joins(:semester_process).joins(:semester_process_volunteer_missions, volunteer: [:contact])
   }
 
   scope :index, lambda { |semester = nil|
     if semester
-      index_joins.where('semester_processes.semester && daterange(?,?)', semester.begin, semester.end)
+      joins(:semester_process).where(semester_process: semester)
+          .joins(:semester_process_volunteer_missions, volunteer: [:contact])
+          .group('semester_process_volunteers.id, contacts.last_name')
     else
       index_joins
     end