Implicit sort order in sms / email notification system

I have an experience as a square customer that seems like it might be an issue.

User journey:

I follow a biz that has random availability. i get notifs on text and email. no matter how soon i click the notif in text, literally within 2 seconds, the appt is no longer available. This has repeated maybe 30+ times.

It is so consistent that i feel like there is an implicit deterministic sort order happening before the notifs are sent, and that the notif service provider executes them in some kind of sequence by sort order - and im reproducibly late in the queue. is this possible?

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