We've run into this issue with replies to texts that the user sent first.

Telecom spam filtering seems to be a ridiculously primitive and wide net. I can't imagine a valid use case for dropping a text sent to a number when that number just sent you a text a few seconds before.

I don't understand why SMS spam has such a big issue with false positives compared to email spam when emails are practically free to send but SMS is much more costly.

(Yes, I know there are a lot of false positives on email too ... but we run into false positive SMS spam issues a lot even though it feels like it should be a much simpler problem to solve).