The issue (“The current input timing is not supported by the monitor...”) still occurs today with the P2425E and U2312HM models. Word has got around about the workaround (disconnecting the power supply). 

When the P2425HE is turned on, are the Latitudes on, in sleep, in hibernate? Test all three conditions.

Instead of off, turn the P2425HE on, then connect the USB-C cable to the Latitudes.

We are having this exact issue too.

Our setup includes Dell WD22TB4 180W docks, which we initially thought were the root cause.  However, after many swaps of equipment and colleague frustrations, as well as finding this post, we are certain it's P2425HE displays.

For the question raised by Chris/community manager, for us it's more when the laptops are woken after going to sleep. 

@Westosha_Net_Eng thank you for posting this here.  Was a solution ever found?

@s1mLM​ We have never found a solution, but I have not had another issue reported to me since last October. When a monitor presents this issue, the only workaround we found was to unplug its power and plug it back in.

My company is also experiencing this issue. @DELL-Chris M can you please provide an update on this! A three p2425he monitor setup with a Dell WD22TB4 dock does not work! Everything is brand new out of the box.

These issues must be registered/recorded through the Support channel to generate Dell cases.

Dell Support must verify the ownership and warranty status. Click the blue "Get Help Now" on the right to start a private live chat session. Share the private Monitor Service Tag and all of your troubleshooting with them.

@tmarciniak​ it appears that Dell want each customer to log this for each device affected, and perform their own troubleshooting.  Despite this clearly affecting multiple customers....

My organisation has already wasted more than enough time on this.

@Westosha_Net_Eng​ We have found that opening the laptop lid, then disconnecting and reconnecting the USB-C connection brings displays back to life.

It's a little better than advising my directors to unplug their monitors every time they return to their desks, but not ideal.

I have a support ticket open with Dell and will post any progress here

Yes, there is some correlation with the laptop being in Sleep or Hibernating mode that triggers the error on the monitor when connecting to the dock. Thanks for the opening the lid trick, I will advise my customers of the workaround. I also created a case with Dell and will post my results.

Ok, a potential fix - to be confirmed.

Dell had responded with a 7 point list of requests of information.  We just don't have the time for that, so I jumped straight to point 6 which was regarding firmware.

They provided a firmware update for the P2425HE display here:

<ADMIN NOTE: Broken link has been removed from this post by Dell>

The firmware shipped with our displays is: M3B101

The update linked above is: M3B102

Version info can be found in the OSD menu.

We have noticed better results immediately during our tests, and are waiting for confirmation from all affected employees.

The update utility only works when connected directly to the display via USB-C (I guess this is why Dell Command Update doesn't update them), and it takes around 8mins to complete per display.

A pity that the symptoms described do not ring any bells with Dell support, as this could have been fixed much sooner, particularly for you @Westosha_Net_Eng 

I should also point out that for a few of our users, they only started getting the symptoms after their laptops BIOS had updated - I'm afraid I don't know which version - but a very recent version as we keep ours auto-updated.

Will give this a day or so with our colleagues to report back.

Hope this helps you guys and others.