Custom property is intermittently not applied while using distribution event

[LyonMartin]

Hi,
We created a Distribution Event Handler to handle publishing events that happens on the server. Inside of it, we have a logic in which it adds custom property for page resources to track its first time published date.
Now we run into a problem that when we publish some pages, they don't have the property we've set. 
And when we try to publish it again, it would show that property.
What could cause that issue?

Thanks and regards!

[kautuk_sahni]

@Vaibhavi_J @Saravanan_Dharmaraj @Kiran_Vedantam @Vijay_Katoch @Sachin_Arora_ @kaikubad @aanchal-sikka @ManviSharma @Shubham_borole @milind_bachani @krishna_sai @manjunathdj  @Siva_Sogalapalli @Manisha_Mirchandani @akhilraj @Nikhil-Kumar  

I seek your assistance in reviewing this AEM question and sharing your expertize. Any guidance or direction you can offer the author would be highly appreciated. Thank you in advance for your support.