I'm having the exact same issue. If I start computer and then plug in Flirc, it will work, but if I reboot, it doesn't work. If I run the Flirc app after reboot, it says the device is disconnected.
FYI, this is the second Flirc device with the same issue. I bought one a few weeks ago, and returned it thinking it was just a defective unit. But the replacement I bought does the exact same thing.
I also have another Flirc, that I bought and set up about a year ago (maybe more) that is working just fine. My comments below describe only my recent experiences, and do not apply to the older, working Flirc device.
I am posting my details (including Ubuntu log entries) in the hopes it will help in finding a solution.
When I installed the Flirc app on my device a few weeks ago, and plugged in the Flirc, the app said there was a firmware update available. However, IMMEDIATELY after it started the update process, the Flirc device disconnected - and the app became unresponsive. Then, I rebooted my system, started up the Flirc app again, and this time it immediately jumped into the firmware upgrade and completed it. NOTE: this happened TWICE - it happened for the device I bought a few ago, and then again when I returned it and bought a new, replacement Flirc.
Now, as stated above, if I start my computer first, and then plug in Flirc, it will work, but if I reboot with the Flirc device plugged in, it won't work. If I run the Flirc app after reboot (with the device plugged in), the Flirc app says the device is disconnected.
My system is running a 64-bit version of Ubuntu 18.04.2 LTS, on an AMD Phenom ii x4820, with AMD Cedar graphics card. Gnome 3.28.2.
The Flirc app states that it is v.3.22.4 with firmware v4.6.3.
After a reboot, the following entries appear in the Ubuntu logs:
10:11:34 kernel: usb usb3-port4: unable to enumerate USB device
10:11:34 kernel: usb usb3-port4: unable to enumerate USB device
10:11:34 kernel: usb 3-4: device not accepting address 5, error -110
10:11:23 kernel: usb 3-4: device not accepting address 4, error -110
10:11:12 kernel: usb 3-4: device descriptor read/64, error -110
10:10:56 kernel: usb 3-4: device descriptor read/64, error -110
Hope that helps.
Let me know if you need any additional info.
Hoping for a quick resolution.