lambda regulations and cylinder misfires?

[AdamE53]

Me again, new issue which is growing.
I've been getting these codes pretty regularly now and i've done some reading but haven't figured out exactly where I should start investigating.
After clearing the codes yesterday, today i'm getting:
CA(202) lambda regulation limit bank 1
CB(203) lambda regulation limit bank 2
misfire cylinders 1, 2 and 3.
Sometimes there will be another lambda code that goes along with those ones and 2 days ago I had misfires across all 6 cylinders.
This issue seems to be growing because the engine light comes on consistently after 5-10 mins of driving and its always a random number of cylinder misfires.
First, if i'm correct, lambda refers to oxygen sensors?
For a bit of history, i've replaced all spark plugs 10,000km ago and replaced the oxygen sensor after the cat appr. 5000km ago.
Any ideas where I can start diagnosing? I have INPA on my laptop so I have the ability to do some basic diagnostic