Fix inference logic

app/models/derived_variables/lettings_log_variables.rb

@@ -247,6 +247,17 @@ private
     if form.start_year_2024_or_later? && (unittype_gn_changed? && unittype_gn_was == 2)
       self.beds = nil
     end
+    if form.start_year_2026_or_later?
+      (2..8).each do |i|
+        if send("relat#{i}_changed?") && send("relat#{i}_was") == "P"
+          (i + 1..8).each do |j|
+            if self["relat#{j}"] == "X"
+              self["relat#{j}"] = nil
+            end
+          end
+        end
+      end
+    end
   end
 
   def get_totelder
@@ -300,7 +311,10 @@ private
   end
 
   def infer_at_most_one_relationship!
-    if partner_numbers.any?
+    new_partner_numbers = partner_numbers.select { |i| public_send("relat#{i}_changed?") }
+    if new_partner_numbers.any?
+      infer_only_partner!(new_partner_numbers.first)
+    elsif partner_numbers.any?
       infer_only_partner!(partner_numbers.first)
     end
   end