Anyone can help me to pinpoint where the problem is?

Anyone can help me to pinpoint where the problem is? See the little gap when the z layer increase? Thanks

What slicing software do you use?

Have you spent time tweaking retraction settings?

@Miles_Wilford using slic3r, will looking into that. thanks

Your retraction is set too tight. Let it retract a bit less and remember to adjust the extra length after retraction!

I don’t know slic3r much. If it was SkeinForge, I would say to look at the clip plugin, which lets you adjust that gap.

Did you get it solved?

@Mano_Biletsky_Open_M a bit improvement, but seems it’s not possible to get it perfect like the other sides, maybe try other slicer to try them out.