This is the VEGA macOS driver or Metal 2 issue in 10.14.5 (and all betas for 10.14.5).... it is, however, fixed in the 10.14.6b2 onwards and in Catalina.
If you render this with a Polaris AMD GPU (e.g. RX 580) it will render 100% correctly in 10.14.5.
I'm suffering with this issue too. Hopefully macOS 10.14.6 will be out soon.