MacBook pro 16 needs power button press to wake

MBP 16, macOS 10.15.3, Thunderbolt 27 display connected via Apple USB-C to Thunderbolt adapter, Apple Magic Mouse, Apple Magic Keyboard. MBP is being used in clamshell mode, with lid closed, external mouse and keyboard used with TB display, like a desktop.

Occasionally, say about once or twice a week, I'll return to my setup to find that the MBP has gone into a really deep sleep. No amount of mouse or keyboard activity will wake up the machine. My TB display is also in sleep mode, but it's the MBP that is the problem. The only way to make it wake up is to open the lid and press the power button. If I open the lid and press one of the built in keyboard keys or use the trackpad nothing happens. I have to use the power button.

When I do this, the machine wakes up. It's definitely a wake and not a boot. Whatever was running before the "coma" is still there - all is well.

I've tried the usual - SMC reset, PRAM reset. I've tried running for a period without the TB display connected and that seems to prevent the problem from happening but I've not run like this for a significant amount of time - I might have jumped to a conclusion, here.

I've tried changing the USB-C to TB adapter. No change.

I work in an office with other TB displays and I've even tried using a different display. No difference.

I've tried disabling the various sleep modes, hibernate modes etc. No difference.

I've used this setup for years, and only recently changed to the MBP 16. My previous MBP 15 didn't show this symptom. But then it was both different hardware and running an older OS - I had not upgraded that machine to Catalina.

So, based on my limited diagnostics, I would say this problem seems to be related either to the MBP 16 hardware/firmware or it's something to do with Catalina. The problem only seems to occur when the lid is closed and connected to a TB display. Cannot firm if this happens with other displays.

Occurrence is random. Sometimes I can go for many days on end without a problem, other times I can get multiple occurrences in a day. Mostly it's once or twice a week.

It's not a deal breaker, but it is VERY annoying after a while.

I've seen lots of other people with similar problems, but I cannot find anything that exactly matches my description. So my guess is that this is Catalina related and not hardware specific, but I'm open to suggestions.

Any ideas?