DisplayPort doesn't wake up from sleep (Catalina)

I've just set up a Lenovo M720Q Tiny using Dortania's Opencore guide. The system works perfectly... with one exception.

After a short sleep, the external display (via DP) will wake up along with the rest of the system when I hit the keyboard or click the mouse.

After a longer sleep (presumably it goes into a different type of sleep), the display doesn't wake up. I have to unplug and plug back in the DP connector to wake it up.

A few details:

• I'm running Catalina 10.15.4.
• Intel i5-8400T with UHD 630 iGPU.
• OpenCore 0.6.1
• Hibernatemode is set to 0.
• I've tried the boot argument igfxonln=1 but this hasn't solved the problem.
• I also tried adding a acpi-wake-type key to DeviceProperties - no improvement.
• config.plist is at https://pastebin.com/R86vqe73 (with PlatformInfo removed)

Any hints gratefully received!