I did get the Media100 RED plugin to open with a less complicated title. You have to wait an unusually long time. I am trying it again with a more complicated RED project and am still waiting. It wasn't like this under High Sierra.
BTW, I'm testing on my 12core MacPro5,1 with 3GB Radeon 7950 and 32GB RAM.
After updating Mojave to 10.14.6, the RED plugin is working better. It's faster than earlier today, but still sluggish compared to High Sierra and earlier. It take about 2-3 minutes to complete launching from Medai100. Once launched, RED's responsiveness is still sluggish compared to Pre-Mojave.
I might attribute some slow down to booting from an external USB3 drive, but it's that same that I used for High Sierra testing.
RED may behave better on newer/faster hardware than my MacPro5,1.