Materials losing their texture after copying another material. (Possibly a bug)

Hi, i have a problem on my project. The first time i open the project my "ground" material loses it's texture, i always solve it by changing it's color on the inspector to something else and then changing it back, however i find it quite annoying to do every time and i don't really know what is the cause of it. I have a script that makes said material to copy other materials so it has different colors depending on the level.

 using System.Collections;
 using UnityEngine;
 
 public class GroundMaterialController : MonoBehaviour
 {
     public Material materialToChange;
     public Material area1Material;
     public Material area2Material;
     public Material area3Material;
     public Material area4Material;    
 
     private void Start() 
     { 
         SetLevelMaterial();
     }
 
     private void SetLevelMaterial()
     {
         // CHECKS FOR GAMECONTROLLER INSTANCE
         if (GameController.instance != null)
         {
             if(GameController.instance.GetLevelNumber() != 0)
             {
                 // SETS AREA 1 MATERIAL
                 if (GameController.instance.GetLevelNumber() <= 5)
                 {
                     materialToChange.CopyPropertiesFromMaterial(area1Material);
                 }
                 // SETS AREA 2 MATERIAL
                 else if (GameController.instance.GetLevelNumber() <= 12)
                 {
                     materialToChange.CopyPropertiesFromMaterial(area2Material);
                 }
                 // SETS AREA 3 MATERIAL
                 else if (GameController.instance.GetLevelNumber() <= 20)
                 {
                     materialToChange.CopyPropertiesFromMaterial(area3Material);
                 }
                 // SETS AREA 4 MATERIAL
                 else
                 {
                     materialToChange.CopyPropertiesFromMaterial(area4Material);
                 }
             }            
         }        
     }
 
     private void OnApplicationQuit()
     {
         materialToChange.CopyPropertiesFromMaterial(area1Material);
     }
 }

All other materials are identical except for the emissive color. I'm using Unity 2019.4.29f1 (but i remember this ocurring on previous versions aswell).