Well you're talking about Kodi game addons:
00:26:50.426 T:1938466736 NOTICE: ADDON: game.libretro.dosbox v0.74.0.107 installed
If you want to use Retroplayer & the Kodi addons stick to Milhouse alpha testbuilds like this LibreELEC Testbuilds for RaspberryPi (Kodi 18.0)
This Remix build is focused on Retroarch, Emulationstation and includes the most common emulators. Kodi game addons use a different romfolder, frontend and cores so they have not much in common.
For dosbox you simply have to copy the dosbox-SDL2.conf file located in \\your_device\Configfiles\dosbox into the dosgame directoy, rename it appropriate, set the correct autoexec commands and your game should run. I've tested it with Elder Scrolls Arena & it works fine for me.
Anyway you find logiles in \\your_device\Logfiles or if you use ssh or winscp in /var/log
After rebuilding I'll add either libretro-uae or libretro-uae4arm to RPi builds as additional cores.
Update:
I've tested libretro-uae & uae4arm and both su... well let's say I'll stick to amiberry for now.