I just got a new HTC M8 from the local Microsoft Store a few weeks ago. For the most part, it is a fantastic upgrade over the HTC 8X I had been using, but it exhibits a few odd behaviors that the old phone never did. The biggest issue is that Cortana's location-based reminders occasionally stop working. The items themselves still show up in the "Remind Me" list, but nothing happens when I arrive at or leave the designated place. Simply restarting the phone does not seem to help, but I've found that I can sometimes get them working again temporarily by disabling Cortana in the app settings (which forces a reboot), and then re-enabling the app after the phone boots back up. I'm not sure what causes it yet, but the location reminders will eventually stop working again, forcing me to go through the process again. My old 8X never had this issue, even when I was using the WP 8.1 Developer Preview.
Even when the location reminders do work, sometimes they're delayed, as though Cortana doesn't know that I've arrived at a place indicated in a reminder. Other apps, like those for maps and driving, have no trouble figuring out where I am, though. I'm wondering if there's a setting that I missed somewhere, or if this is indicative of a more serious hardware malfunction that will get worse over time.
Has anyone else seen anything like this?