Currently playing through this game.

I have experienced a LOT of issues with;
1. Graphical distortion - Primarily only the top half of text was being displayed when counting up the collected booty.

2. S-L-O-W movement of your little king.

3. The game crashing randomly - This would occur at the worst time; either loading into the castle, sitting in the throne, after beating a king (before the cut-scene plays) - basically after a lot of hard work & just before I could save my progress.

4. Unable to successfully load a save file - This occurred for me A LOT - I'd start the game, select my load, be presented with a blank/black screen... I'd have to alt-tab out or the game game and close it via the task manager before trying again... It would often take a good 20-50 mins (of loading/crashing/closing over and over) to get into a game.

5. Achievements not unlocking.

For me, the solutions were;

Issue #1 - Was to keep the setting resolution at 1080 - The issue only occurred when the res was set to 4k.
Due to the graphics style & source there's not a huge improvement in setting above 1080

Issue #2 - If found using 60fps with v-sync enables caused lots of movement slowdown.
I found 60 fps without V-sync was fine - Though, personally I stuck to 30fps (just in case).
(The slowdown causes timing issues when facing enemies (your guys can't get out of the attack radius in time)
& using the lift - My little King refused to enter the lift at 60fps with V-Sync enabled).

Issues #3, #4 & #5 - Do NOT use the default loader... instead use LittleKingStoryXp.exe.
This can be found in the [game install path]\Little King's Story\LittleKingStoryXp.exe

Using this loader...
- Save games now load first time every time.
- The number of in-game crashes experienced have been significantly reduced.
I do still get the occasional crash (notably after beating King Long Sauvage, just before the cut-scene/in-game animation is played - crashed the first time, worked the second)...
But overall a much better experience.
- Achievements are now awarded (including those I unlocked when playing via the default loader)

I've not yet finished the game - So there may be issues I've yet to experience.
But using this approach has made my experience immeasurably better.
Hopefully this will help others have a more enjoyable experience of this amazing game :)

TL;DR
1. Don't set the game to a resolution above 1080.
2. Don't use v-sync if you have fps set to 60.
3. Don't use the default loader, instead use LittleKingStoryXp.exe.