Which is usually a fair indicator that all is functioning within satisfactory parameters.
Warnings are typically just that – warnings, rather than errors – and can often be simply ignored.
As to the warning itself, one can only guess. It may be for example that EDID is malfuntioning, or that the monitor is too old to use that technology, or it could be something else altogether.
As you may be aware, there have been many difficulties with the Nvidia 580xx series drivers, and I’ve seen mentioned that the 590xx series isn’t expected to be much better.
For some users it has been suggested to use the Nvidia 570xx or 575xx series instead. Take a look through the recent Stable Update threads for further information.
Recent Stable Update threads:
That said, my opinion is that if there are no obvious issues, then perhaps you are among the “lucky ones” that seem to have largely escaped those particular problems.
Regards.
No doubt providing your system information will allow for more specific responses:
System Information
While information from *-fetch type apps might be fine for someone wishing to buy your computer, for Support purposes it’s better to ask your system directly; 
Output of the inxi command (with appropriate parameters, and formatted according to forum guidelines) will generate information useful for those wishing to help:
Suggested inxi command (use either):
inxi -zv8 |
(short-form) |
inxi --filter --verbosity=8 |
(long-form) |
inxi man pages |
(manual) |
Running `inxi` within a `chroot` environment
- Add
--color=0to the long-form command, or… - Change the short-form command to
inxi -zv8c0