Strange delay in campaign sequence

I have set up a campaign using Internal Form Submitted as a goal. Upon form submission, there will be a tag assigned to the contact and there’s a small delay of 1 minute. After that, another sequence will trigger a HTTP post to a 3rd party service to send a SMS message. Once that’s done, system creates a note and also remove a tag.

Inside “Assign SMS tag” sequence

Inside “Twilio SMS test” sequence

In this following screenshot, the first time I submitted the internal form, the campaign sequences worked as expected. (( Form submitted at 5:00pm ))

However, when I submitted the same internal form again 3 minutes later, the first sequence “Assign SMS tag” was held up in “Active Sequence” queue and was scheduled to run 15 minutes later. (( Look at the difference in time stamp. Form submitted at 5:03pm, campaign sequence ran at 5:18pm ))

I don’t understand how that happened. Was there a special rule for my use case?
I did a few tests and noticed there’s always a 15 minutes queue between each time I submitted the internal form.

Infusionsoft has a hard-coded delay of 15 minutes if you are trying to apply the same tags to the same contact in quick succession. The campaign will work as planned for one-time though people, but when testing with the same contact over and over it will cause the delay.