An NPC in estrus that leaves the map can call ShouldBeInEstrus upon loading the save later, so initialize there if needed.

1.3/source/RJW_Menstruation/RJW_Menstruation/HediffComps/HediffComp_Menstruation.cs

@@ -1127,6 +1127,8 @@ namespace RJW_Menstruation
 
         protected virtual bool ShouldBeInEstrus()
         {
+            if (!loaded)
+                Initialize();
             switch (curStage)
             {
                 case Stage.Follicular:

changelogs.txt

@@ -1,5 +1,6 @@
 Version 1.0.7.5
  - Fix error when one womb's concealed estrus is overwritten by another womb's visible estrus.
+ - Fix error after the game is loaded with an NPC in estrus off-map.
  - Fix missing texture error when insect egged with multiple sizes.
  - Properly calculate cramp pain falloff again.
  - Climacteric and menopause are now per-womb, appearing in the womb dialog instead of as hediffs. Any old hediffs should disappear upon loading the save.