Extrusion gap near seam/deretraction  

You are printing external perimeters first and using Arachne.  Try Classic and disable the external first option so there is more support for the outer perimeter start.

Cheerio,

RE: Extrusion gap near seam/deretraction

If I print with no infill the gap issue is mostly gone (third print in image below). There must be something in the perimeter slicer algorithm that's causing this defect. It'd be interesting to have someone that works with the algorithm look at what might be causing this.

RE: Extrusion gap near seam/deretraction

You are using a 0.6mm nozzle.  There are many posts and issues relating to this problem with the larger nozzles.  For a start more filament leaks during travels so when it moves from the end to the start it is missing filament and hence the gap.  

https://forum.prusa3d.com/forum/prusaslicer/seam-gaps-in-bigger-nozzles/ for example

You have a long travel to the start of each layer if you look at the preview.  You could try changing your seam settings to nearest which should reduce travel.  

There are other settings you could also experiment with such as turning off the wipe while retracting or possibly adding on a small Deretraction Extra Length, although that could cause problems in other areas.

RE: Extrusion gap near seam/deretraction

Interesting. I've read through several of these posts but just haven't been able to grasp what exactly causes the printer to do this. Can you expand a bit on what you mean by "leaks" and "missing filament" please?

RE: Extrusion gap near seam/deretraction

Do some research and read through some old threads.   Filament at temperature is effected by gravity.  Gravity makes things fall down.  Filament falling down 'leaks' out of the nozzle.  The bigger the nozzle the more you will see it happen.  Retraction pulls filament back up the nozzle to counteract this.  But leave it long enough and it will leak a tiny bit.  When the nozzle travels and isn't printing it can happen. Wispy filament strings, leaky filament.  If the travel cross inside your object it catches on the infill so you wont see them.  Travel from one island to another or one model to another and they are outside the print and visible.

RE: Extrusion gap near seam/deretraction

Thanks so much for the recommended settings and detailed explanation. The nearest seam setting is something I'll definitely be defaulting to now. Do you think the pressure equalizer settings, slope negative probably, would have any effect on this phenomenon?