How to reproduce

1. Place an item frame with an item in it
2. Run the following command 

   /data merge entity @e[type=item_frame,sort=nearest,limit=1] {Item: {components:{"custom_name": '{"text":"Hello"}'}}}
   

3. Notice that the item was given the custom name as expected
4. Run the following command to change the custom name

   /data merge entity @e[type=item_frame,sort=nearest,limit=1] {Item: {components:{"custom_name": '{"text":"World!"}'}}}
   

5. The item wasn't renamed, the command silently failed, and an error was logged to the console

   [00:45:25] [Server thread/ERROR]: Tried to load invalid item: 'Duplicate entry for key: 'b[type=minecraft:custom_name, removed=false]' missed input: {custom_name:'{"text":"World!"}'}'
   

6. Now run the following command to rename the item, including the minecraft: prefix

   /data merge entity @e[type=item_frame,sort=nearest,limit=1] {Item: {components:{"minecraft:custom_name": '{"text":"World!"}'}}}
   

7. Notice that this worked