I noticed while booting up first is shown OpenELEC, than LibreELEC and at the end KODI logo. This is due the fact that I migrate / upgrade the system from OpenELEC to LibreELEC and some system files are left behind? Best would be a clean install from scratch? Would that speed up a little bit the Kodi interface?
The very first logo you see is an u-boot logo. OE logo was flashed on your device by one of my early releases, I dropped flashing logo some time ago. If you want to revert to default logo (manufacturer-provided), you should extract logo.img from Android firmware, copy to your device and dd it do /dev/logo. For example, if you put logo.img to Downloads folder, you should execute dd if=/storage/downloads/logo.img of=/dev/logo.