Been doing some small adjustments to the derailer using the 2 screws and the adjuster on the gear selector on the handle bar, managed to get every gear up and down, it couldn't be any better aligned with each cog in the cassette, however the chain persists in jumping out, the chain did slip off the cassette altogether at one point so adjusted the limit screw to stop that. Looking at the cassette itself................ As you slowly rotate the pedal with the bike raised off the ground, the 2nd smallest cog looks like there's adequate spacing, however as you watch it rotate, the spacing seems to get thinner/closer at one particular part, as said I am no expert, but that suggests the issue lies with the cassette itself??