I had placed a Particle Tracker One in shipping mode using the console command {"cmd":"enter_shipping"} prior to travelling to another region.
Upon arrival I plugged in the device to a USB-C powered connection and the device booted up, blinked the charge light very rapidly for 3 secs, and then it went out. The device is not charging at all, the moment I unplug the device turns off. The device itself functions perfectly when its plugged in.
I believe a rapidly blinking charge light means there is insufficient current but I have tried different cables/options to no avail. Why does it not want to charge?
It sounds like the battery became disconnected. It could be as simple as a loose JST connector.
Under normal circumstances the battery will still have charge after months in shipping mode. Even if it discharged, the charge light should go on solid until charged, then the charge LED will turn off after the battery is fully charged.
If the charge LED flickers wildly, it's typically because the battery is not connected. Device OS turns off charging at that point, and will retry periodically so you'll probably see it blink occasionally.
There's a slight possibility that the battery pack failed, but that typically causes the charge LED to blink, not flicker wildly, and it will continue to blink forever.
If you do open the Tracker One to inspect the battery connector be careful removing the top because both the LiPo battery and the NFC antenna are glued to the top of the case. The NFC cable is shorter than the battery cable.