Sims 4 causes severe system lag (not in-game lag)

I've narrowed down the severe system lag to only when the game is minimised in the Dock. If the game is running in windowed mode in the background I can happily have loads of apps open and the OS manages resources as expected - smoothly and seamlessly. Once the game is minimised it affects everything else running including other minimised windows.

I have tested on three Macs:

2017 15" MacBook Pro

3.1 GHz Quad-Core Intel Core i7

16 GB 2133 MHz LPDDR3

AMD Radeon Pro 560 4 GB

Intel HD Graphics 630 1536 MB

512GB SSD

2019 27" 5k iMac

3.6 GHz 8-Core Intel Core i9

32 GB 2667 MHz DDR4

AMD Radeon Pro 580X 8 GB

512GB SSD

Mid 2012 15" MacBook Pro

2.6 GHz Quad-Core Intel Core i7

16 GB 1600 MHz DDR3

NVIDIA GeForce GT 650M 1GB

Intel HD 4000 1536 MB

480 GB SSD

And running the following versions of macOS either internally or on external bootable drives:

macOS 10.15.3 beta build (19D75a)

macOS 10.15.2

macOS 10.14.6

It happens on both Macs with AMD GPUs but not on the Mac with NVIDIA. It happens with CC and with a clean game folder. Also in a new clean install.

There are also annoying lines across objects in-game in full sunlight. These are worse on the Macs with AMD than the one with NVIDIA. These two issues seem to be interconnected but I couldn't say for definite.