Hi,

Recently I noticed an issue with my dual monitors configuration. I used to have my monitors sleeping after 5 minutes of inactivity, as setup in gnome control center. 
When I changed them, the behavior was not that described anymore. It is not related to the monitors as far as this sleeping feature works with an other OS. The difference between the new ones and the old ones *may* be the DPMS feature.

The new behavior observed is: 
- after X minutes of inactivity, monitors go black 
- instead of having a "no signal" popup, monitors re-up after few seconds 
- after X minutes again of inactivity, monitors go black again 
- etc
I get the same by typing xset dpms force off.
When I try this with only one monitor connected, it goes to sleep as expected.

The fact is, after seeking for hours in forums, I found that : https://askubuntu.com/questions/1047182/dual-monitors-on-18-04-with-radeon-rx-580-gpu. And for an unknown reason, despite the fact the issue described there does not seem to be related to mine, disabling the DC layer of amdgpu works! In other words, after X minutes of inactivity both monitors go to sleep as expected.

I hope this is not to confusing.. it is quite hard to describe as a non-english native person.

Cheers.

PS: my 'uname -a' returns Linux XXXX 5.8.0-45-generic #51~20.04.1-Ubuntu SMP Tue Feb 23 13:46:31 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux