Placement of 了: difference between 吃飯了 and 吃了飯 Do 我吃早飯了 and 我吃了早飯 mean the same thing (I have eaten breakfast), slightly different things? Or is one of them wrong? Which is better? 

(For context, the second option was marked incorrect by an app and I can't figure out if it's a problem with an app or something I don't understand.
From my answer to this question:


  Example cases with 了
  
  
  了: aspect marker, indicating completed action. 
  了: final particle, indicating change of situation.
  了: final particle, indicating sentence has ended; emphasize sentence; soften tone
  


我吃了早飯:


了 is an aspect marker indicating completed action when it is following a verb but not at the end of a phrase, therefore, 我吃了早飯 can only mean "I've eaten breakfast" (the verb 吃 is completed)


我吃早飯了 :


If 了 is treated as a aspect marker, the sentence would mean "I have eaten breakfast" (the verb phrase 吃早飯 is completed)
If 了 is treated as a final particle (indicating change of situation), the sentence would mean "I (now) eat breakfast (from previously not eating breakfast to now eating breakfast)
or  more likely, 了 indicates 1. the sentence has ended,  2. adding emphasis or soften the tone of the sentence


"我吃早飯" sounds blunt and make the sentence sound incomplete

In "我吃了早飯了", the first 了 indicates the verb 吃 is a completed action and the second 了 indicates the sentence is finished (also emphasize the sentence / soften the tone)