Just thought I'd pipe in here. I'm happy to help in any way, but I can confirm that Cura gets almost unusable for me after which I need to restart it. It then works great for a while then gets more and more slow until i have to close and restart it. Here are my computer specs:
System: Mac Pro (mid 2010)
OS: Mojave 10.14.2
Mem: 64GB RAM
CPU: 12-core 3.33GHz Xeon
GPU: Radeon RX 580 8G
Printer: Ultimaker S5. Firmware 5.4.27.20191212
Cura: 4.3.0
FWIW, I had the same issue when using BCN3D Cura with my Sigma and Sigmax, but I know that's