Mounting manually to:
"sudo mount /dev/sda1 /media/usb" (instead of usb0)
and restarting emulationstation doesn't trigger USB ROM Service as well.

Also checked other pen drive. Same issue. Checked same raspberry pi with other OS on other card (OSMC). No issue. It's strictly Retropie OS issue!

The next one will be a Pi 3 B so I can have the option to include PS1 and N64 games as well as flexibility to try a bunch of other IoT stuff that's been on my mind for a couple years. :)

AlexMurphy is right, check out that link. It very well could be (as the link states) that your power supply isn't providing enough current. Also, if you are running a pi 3, if my memory serves me, wifi is built in. You not giving us any base information to work with makes things difficult to help.

Also, if a better power supply doesn't work, I'm guessing that it's a hardware issue, not software, in which case, this is probably the wrong place to ask.

@dankcushions Thanks for that link. I will try it.
Right now when I booted up the Pi it "mounted" the ROMs perfectly. So it seems to happen spontaneously - weird.

I wanted update the manual way for anyone who needs to fix this in the future.

To run the script file you need to ```
sudo bash ~/RetroPie-Setup/retropie_setup.sh

Once the script runs 1. Manage packages 2. Manage core packages 3. retropie menu 4. update from binary If your missing the RetroPie-Setup directory, sorry you're going to have to reinstall. Hope that helps someone!

Changed fstab to:

proc /proc proc defaults 0 0
/dev/mmcblk0p1 /boot vfat defaults 0 2
/dev/mmcblk0p2 / ext4 defaults,noatime 0 1
UUID=1918-2A41 /media/usb0 vfat auto,nofail,noatime,users,rw,uid=pi,gid=pi 0 0

/media/usb0/BIOS /home/pi/RetroPie/BIOS none auto,nofail,noatime,users,rw,uid=pi,gid=pi,bind 0 0

/media/usb0/roms /home/pi/RetroPie/roms none auto,nofail,noatime,users,rw,uid=pi,gid=pi,bind 0 0

more streamlined and I think 'bind' in the first of the three additional lines was the cause.

@jonnykesh said in Boot Script ordering for USB Mount and SplashScreen:

@hooperre Have you considered turning the custom splash screen into a static video file? say 5 or ten seconds, whatever you feel is best.
You say videos on the USB work fine so just turn the static image into a video file.

Truth. Good shout. I'll probably just put them on the SD card unless I can dig into the splashscreen stuff and find out how to have it start later? Not sure. I know using Filezilla if I attempt to change permissions it doesn't work and I can't add them, but I know I can do it with Putty (chmod) it works. That's the only reason I preferred to stay on the USB.

@herb_fargus It's not a 3rd party image, it's someone's preconfigured noobs setup with 3 partitions: one with Retropie, one with Kodi, and one with Raspbian. It's still the default Retropie image on top of a headless raspbian os. It was done this way so you would have less overhead when running Retropie (rather than having Raspbian with the GUI with both Kodi and Retropie installed and running on it).

Sorry, I think it's working just fine.

It's just that I thought that because I could access Retropie roms folder via LAN and see all the roms, that meant that they were on the SD card, but what I was actually doing was accesing the USB drive roms folder.

Sorry!