Thanks Gianni!
I am referring to this forum post specifically: On Create registrant, comments, custom_questions or other data isnt saved or cant be accessed
And, upon further research, I’ve noticed the issue is different than what I initially observed it to be.
Originally, I was under the impression that the custom_questions field was having a specific issue and not storing the information submitted to it via the Zoom API. That is, when I pull the registrants info via the API, the custom_questions field returns an empty array:

However, upon further review, it has come to my attention that fields that were previously storing data are no longer doing so. Specifically, the "phone" and "org" values are not being populated even though they had been previously. During my investigation I remembered that in the past, when "org" and "phone" were not present, I was able to fix this issue by sending a PATCH request to the meeting itself (meetings/{meeting_id}/registrants/questions) submitting "org" and "phone" in an array called "questions" :

As you saw above, now "phone" and "org" are also missing from the Zoom API return. What’s more is if I use the exact same function/code to register for a meeting that was created a few months ago, the "phone" and "org" values are properly filled. Any ideas as to why that might be?