I booted up the new APU1C4 from PC Engines last night with RouterOS 6.12

How?

I tried with netinstall, but there is no results.
Also, i tried with usb cd-rom connected to apu... no results....

It is not need to change previous script. I tried it on RB411UAHR + Sierra Wireless MC8775 and it works. USB became active after 2-3 auto-reboot

Almost every time (I'd say 9 out of 10) I shutdown the router, disconnect the power, and boot up again, the usb port (under system) comes back invalid. A reboot rectifies the problem. This basically means that every time I power up and boot, I have to reboot. It's not really really a problem. Just ...

*) ppp client - fixed possible loss of configuration after reboot for some modems; Still have bug. For some modems, after reboot, I see another ppp-cli interface (disabled, ppp-out1, added by router). Previously configured ppp-cli interface points to the unavailable usb port, because router increas...