Plenty of weird error stuff is going on there...
I'd say do a full re-install of LibreELEC 9.2.2, and forget about skins and other add-ons.
Enable debugging and restart LibreELEC.
Then play one of your (problem) videos, and provide a new log file.
You could also run a DIMM memory checker, just in case. Any Ubuntu Live distro should have one of those on board.
There is likely a bug in the thumbnail processing of pictures, something that already existed in earlier RPi3 releases as well. And something that hasn't been able to fix just yet.
Or is it crashing on already thumbed pictures/photos? If so, can you provide a sample or two of them?
Generic 9.2.2 is out now.
The simple way for me to upgrade is via SSH'ing into the Kodi device, and then:
- cd .update
- wget LibreELEC-Generic.x86_64-9.2.2.tar
- reboot
Which add-ons specifically? Because I don't know any add-ons that cause reboots.
You could try copying the EDID file from the TV/monitor via the getedid script, here is how: Custom EDID [LibreELEC.wiki]
Analog video signals and CRT screens are a whole different ballgame, I remember them. 
if I start my Raspberry before starting my TV, then the image is bigger than my TV
If the RPi has no EDID info from your TV, then it'll start to make guesses.
Also your TV should have a setting for handling PC signals properly, so overscan will not happen.
2020-03-21 18:48:25.396 T:1816114048 WARNING: No information found for item '/media/My Book/TV/Tom Clancys Jack Ryan/Jack Ryan S02E08.mkv', it won't be added to the library.
if you want to use Kodi's default scraping, it's best to stick to default named folder setups. Typos can mess things up too.
I use: //server/TVSHOWS/Tom Clancy's Jack Ryan/Season 2/Tom Clancy's Jack Ryan - S02E08.mkv
and it's picked up with no hassle.
My RPi 3 is connected via 1000 mbit LAN
Unfortunately for you, the RPi3 only has a 100Mb/s port, which works at approx 30-35Mb/s as per USB2.0 speeds.
The RPi4 has a gigabit port, it that works at 300Mb/s speeds. Still better than a RPI3, and the RPi4 has more 'oompf'.
Also select the Arial font in the Kodi GUI. This is an option in Estuary and perhaps other skins too. That font holds many more characters.
Do you have "Wait for network" enabled in the LibreELEC Settings add-on?
My Pi gets power from the USB-output from the TV.
A typical USB 2.0 port will only provide 0.5 Amps per port. The RPI4B needs upto 3.0 Amps, that's quite a difference. The RPi3 is not that power-hungry. You might trash your TV's usb port in the end if that USB port is strained for so long.
Get yourself a decent 3.0 / 3.5 Amps power adapter. The RPi4 will probably simply not get enough juice/power to boot up properly.
e Raspberry Pi 4 generates a lot of extra heat as compared to the Raspberry Pi 3. You might want to make sure the RPi 4 has sufficient cooling.
There is a (first) firmware update which should keep the RPi4's CPU a little bit cooler. Install it.
Overscan is to be solved via your TV settings.
"Last version" is not an official version.
And also, LibreELEC 9.2.1 with Kodi 18.6 has been released.
Is this a known thing with the RP4 ?
Nope.
can I then boot my Pi 4 into LibreELEC from my USB?
No. Unlike the RPi3B+ which can boot from USB, the RPi4B does not support booting from USB (yet).
You can boot from the SDcard and use USB as a subsequent system and storage drive. There are tutorials for that online.
It's a old-ish video card... circa 2-3 years old..
"So which car do you drive?"
"A red one".
I've tried.
Old or new Nvidia card? Don't be shy giving details, we're not sitting next to you.
What hardware+graphics did you install LibreELEC on?
