What are the causes of step loss

I own a Chinese 6040 CNC which I bought around two years back. I have been using this machine to cut aluminum and plastics and cant remember having any accuracy issues. Last week I was cutting aluminum and see various accuracy issues. I guess these issues are caused by step losses?

To see if these are caused by motor loading, I changed my work piece to machine wax from Aluminum with no luck. Then I slowed down cutting to 30% of above feed rate. Although things improved, I still get issues like incorrect dimensions and uncut regions in side walls at lower Z levels. I Also changed some settings such as BASE_PERIOD, max velocity etc with no luck.

In order to first isolate the problem, I would like to know if step losses can be cased due to software issues such as wrong configs? This machine uses 2M542 stepper drivers which seems like a Chinese clone of Leadshine drivers. What else can I do to isolate this?

If it worked before without issue it may be a mechanical problem
( loose couplers being a common issue )

yes! X axis coupler was loose. I fixed it and will be milling the next part soon. Hopefully this fixes the issue.
Cheers!

Of corse bed configs is most possible reason. Check latency test for your machine.
Also be shure if your computer doesn't turns on any screen savers also.