I have that machine. Take it back to the dealer and show them your samples. It looks like it needs to be recalubrated.

Same issue with my newly purchased Janome MC500E, that I just bought a month ago. But It is not stitching properly. Don't know what's the reason. Even I performed all the necessary steps including changing needles, bobbins, etc. but facing same issue. Therefore, posting here to get the solution. Thanks.

Successfully solved the stitching issue after watching YouTube tutorials and reading blog posts. No it is stitching clothes efficiently. My friend helped me in solving this. Thanks.