TL;DR: After a power loss, Entware installation and all my user scripts on the USB were gone. Had to reinstall them all.
I installed 386.4 over 386.4 beta 2 a week ago and everything were running smoothly. After an unexpected power loss the other day (power line damaged by construction workers), I noticed that my router was not running any of the scripts on the USB, as well as the Entware. WAN connection was there, all the settings were the same but none of the scripts were executed and add-ons tab was missing. So, I rebooted the router via GUI to fix issues but to no avail.
Trying to SSH into the router threw an "SSH key/fingerprint does not match" error, so I've manually edited my ./ssh/known_hosts and after that I was able to connect to router without a problem. Once I got connected, ran "amtm" and none of the scripts were there, it was like I was trying to install scripts to a vanilla Merlin firmware.
I've installed all the scripts one by one, starting with Diversion which read the backup files successfully, and now everything is back to normal even after a couple of reboots (via GUI).
Sadly, I don't have the log files for when the incident occurred but I'm pretty sure USB is not the cause.
My network is simple: Several LAN Devices -> AX58U (Router Mode) -> DOCSIS 3.0 Cable Modem (Bridged) -> The Internet
Just wanted to share my experience to see if anyone had the same issue.
PS: Thank you RMerlin for your hard work.