The yellow borders/coastlines do not fully render, but only partially render, leaving them fragmented.

If this is the OP then this is what my 'no fix' is referring to. Legacy gives me full (non broken) rendered lines.

I should probably made a separate post for the map layer render in general ...

No fix 1463 CIV. Slow render of map layers in general (mostly Sentinel). Legacy 1.5 works perfect.