Chain slipping off from singlespeed rear cog

After I have worn out the cogs and chain to the point where my chain tensioner couldn’t keep up anymore, I have replaced my drive train pieces, the axle and spacer are still the same.

So I went from:

• unidentified front wide/narrow chain ring (42T)
• Gusset 1-er converter 15T
• SRAM PC-830 (114 Links, 8speed, 3/32″)

to:

• absoluteBLACK CX Round wide/narrow chain ring (42T)
• Shimano CS-MX66 3/32″ sprocket 14T
• Connex 8SX Chain

I switched from 15T to 14T, there is the usual winter surface grime on it (and cleaned up twice already) and switched the chain/sprocket combination because the Gusset conversion kit seemed a bit too wide for being on spec.

That said, ever since I changed parts my chain keeps slipping off the rear cog and already brought me twice into dangerous situations. I’ve looked around and tried to eliminate the causes, the chain is straight, the spacers on the conversion kit are just like they always have been, the pieces should individually fit. The new chain is a around half the weight of the SRAM chain.

Pictures:

• 1st Bolting, 2nd Tensioner, 3rd spacers, dashing is the freehub (approx):
  

• Order of elements:
  

• Closeup:

• level clamped to chainring to ensure the chain is straight:
• axle picture when I initially bought the bike with the original parts:
• picture with chain installed: