I bought a new MBP 16" base model last week. I can reproduce this behavior 100% on Catalina 10.15.5:
(Independent if power nap is on / off)
First thing I noticed and was able to reproduce:
1. Connect the MBP display to an external Monitor (I connected it directly with a DP -> Type C) cable. (It doesn't matter which port on the MBP).
2. Close the lid of the MBP. Everything is working as it should at this point in time (external Monitor).
3. Put the MBP in to sleep (Apple logo in the upper left corner -> sleep)
4. Wait for about 4-5 minutes.
5. Try to wake the MAC with external peripheral (in my case apple magic keyboard)
Result:
Screen of external monitor stays black. When opening the MBP it is completely dark (touchbar, keyboard light, display). It gets hot in the upper keyboard area. From there on there are only two ways out:
1. Wait about 5 minutes and the MAC restarts itself
2. Force restart
Second thing I noticed:
1. Connect the MBP display to an external Monitor (I connected it directly with a DP -> Type C) cable. (It doesn't matter which port on the MBP).
2. Close the lid of the MBP. Everything is working as it should at this point in time (external Monitor).
3. Put the MBP in to sleep (Apple logo in the upper left corner -> sleep)
4. I can't exactly specify the amount of time it has to stay in sleep (in my case it was overnight)
5. Open the lid of the MBP (external display still connected)
6. The MBP restarts (immediately shows startup apple logo)
I didn't have any of this issues on my MBP 13" - so I suppose it has something todo with the dedicated graphics card. It is very frustrating and I will likely send it back next week.
I don't have any of this problems when using the laptop without external monitor. On 10.15.4 I noticed one kernel panic when opening the lid from sleep without an external monitor - but this issue was resolved by disabling power nap.
I bought this machine at this point in time because I thought, the fact it was released last year makes it more likely that such issues are resolved by now (half a year later!). But the fact that such hiccups are not resolved makes me doubt they are going to be resolved at all. Maybe it is just time to move on frome apple.