Condition 2: Gang Lun owns Reading Steiner, even if the world line changes, both Gang Lun in 2025 and Gang Lun in 2010 retain the memory before the world line changes.
Question: Gang Lun in 2010 has the memory of saving his assistant, but Gang Lun in 2025 only has the memory of sending D-mail, not the memory of 2010 on this world line. However, Gang Lun in 2010 will have the memory of 2010 until 2025. Therefore, in 2025, he fell into a dual state of having the memory of 2010 and not having the memory of 2010. it's out of the question.
Supplement: Not just the ending, every D-mail has such a contradiction.
Guess: In order to solve this contradiction, one of the possibilities is that the world line "shrinks", and Gang Lun must have amnesia between 2010 and 2025.
View more about Steins;Gate reviews