diff --git a/app/models/users/scopes/having_reminder_mail_to_send.rb b/app/models/users/scopes/having_reminder_mail_to_send.rb
index 24d03c4ca0b1..0b59bce243f4 100644
--- a/app/models/users/scopes/having_reminder_mail_to_send.rb
+++ b/app/models/users/scopes/having_reminder_mail_to_send.rb
@@ -175,7 +175,8 @@ def build_local_times(times, zone)
       end
 
       def quarters_between_earliest_and_latest(earliest_time, latest_time) # rubocop:disable Metrics/AbcSize
-        raise ArgumentError if latest_time < earliest_time || (latest_time - earliest_time) > 1.day
+        raise ArgumentError, "#{latest_time} < #{earliest_time}" if latest_time < earliest_time
+        raise ArgumentError, "#{latest_time} - #{earliest_time} > 1 day" if (latest_time - earliest_time) > 1.day
 
         # The first quarter is equal or greater to the earliest time
         first_quarter = earliest_time.change(min: (earliest_time.min.to_f / 15).ceil * 15)
diff --git a/app/workers/cron/quarter_hour_schedule_job.rb b/app/workers/cron/quarter_hour_schedule_job.rb
index dc4cc9e66eb9..dc9b7b93b13f 100644
--- a/app/workers/cron/quarter_hour_schedule_job.rb
+++ b/app/workers/cron/quarter_hour_schedule_job.rb
@@ -52,16 +52,19 @@ module Cron::QuarterHourScheduleJob
   private
 
   def upper_boundary
-    @upper_boundary ||= GoodJob::Job
-                          .find(job_id)
-                          .cron_at
+    @upper_boundary ||= good_job.cron_at
   end
 
   def lower_boundary
     @lower_boundary ||= begin
+      # The cron_key is used here to find the predecessor job.
+      # The job_class has been used before as a comparison but this fails in
+      # the SaaS environment where multiple tenants exist. The cron_key gets the
+      # tenant information prepended and is thus scoped to the tenant.
       predecessor = GoodJob::Job
                       .succeeded
-                      .where(job_class: self.class.name)
+                      .where(cron_key: good_job.cron_key)
+                      .where("cron_at < ?", upper_boundary)
                       .order(cron_at: :desc)
                       .first
 
@@ -72,4 +75,8 @@ def lower_boundary
       end
     end
   end
+
+  def good_job
+    @good_job ||= GoodJob::Job.find(job_id)
+  end
 end