Index: app/models/time_entry.rb
===================================================================
diff --git a/app/models/time_entry.rb b/app/models/time_entry.rb
--- a/app/models/time_entry.rb	(revision 30ed1a4be268d5b863ac736176dd275c08a54b2a)
+++ b/app/models/time_entry.rb	(date 1617630564995)
@@ -113,6 +113,13 @@
             self.project_id = issue.project_id
           end
           @invalid_issue_id = nil
+        elsif user.allowed_to?(:log_time, issue.project) && issue.assigned_to_id_changed?
+          tmp_previous_assignee = issue.assigned_to
+          issue.assigned_to = issue.previous_assignee
+          unless issue.visible?(user)
+            @invalid_issue_id = issue_id
+          end
+          issue.assigned_to = tmp_previous_assignee
         else
           @invalid_issue_id = issue_id
         end