Because someone will ask for a screenshot eventually, here it is up front:
This app has been deployed and used by 95 of our users (University Faculty) to select new computers. There is a Flow that should run when that button is clicked which basically sends them an email with a summary of their order. For a small number of them (9 as of a few minutes ago), their orders are being created, but the Flow is not firing. We had one user early on for whom the Flow started but then failed. In that case, there was something wonky with their Connections in Flow. In these other 9 cases, though, the Flow never even initiates.
Unfortunately, I'm not even sure where to begin diagnosing or troubleshooting the problem. I suspect that it's probably similar to that first user (broken/missing connections in Flow), but it's just odd that it's not even trying to run.
It would be much appreciated if you could share some information about the failing flow information.
For how to troubleshoot a flow, see:
For the flow not trigger in PowerApps, there should be error messages showing out at the top of the App screen.
Basically it should be the LastRecord collection, make sure there are data within it before the flow executing.
For example, we could switch the formula as below:
If(!IsEmpty(LastRecord), Flow.Run(First(LastRecord).ID), ErrorReminding)
Please define your own error reminding information.
Actually, I discovered that the problem was carbon-based. That is, the users were exiting the App without clicking the gigantic blue "Submit" button that would have triggered the Flow. Their "order" was actually created on a previous screen, so the Submit button really just updated some info in that record and kicked off the Flow to send them an email.