HP U28 4K HDR Monitor 1Z978AA#ABA - USB-C issues when connected to iMac (no wakeup, no video)

[Scaramoosh]

Bought monitor new two weeks ago. Arrived today, installed it today.

Monitor is connected to an iMac/2019 (iMac19,2) running Monterey 12.0.1 over USB-C - using the HP USB-C which came on the box (after reading all the warnings on the product manual about USE THE CABLE THAT COMES WITH THE MONITOR - yes, the manual which doesn't come in the box but you have to download as a PDF - if you can find it on the support site.)

Since then, two issues:

1) when iMac goes to sleep, and then I wake it up - U28 *does NOT wake up*. I have to turn it off, on again.

2) After a reboot - it just disappears. It says "no connection", iMac doesn't even see it. Tried:

2.1) turning off, and on - NO DIFFERENCE

2.2) turning off, removing power cable, wait 15 seconds, turning back on - NOPE

2.3) turning off, changing USB-C connection to the OTHER USB-C port, turn back on - YES

I find extremely infuriating and very concerning that this monitor just seems not to know how to work w/ a Mac - no support for sleep/wakeup, and just disappears after a reboot ?

A quick search on the forum shows these issues are common with the combination U28 + Mac. Just posting this here for (a) future reference to other users which may run into this too, and (b) (long shot) if someone from HP support actually sees and attempts to reply.

This baby is going back tomorrow . . . I spent $450 + extended warranty, bought because of the brand. I should have gone with a low-end brand, will probably have the same issues, but at 1/3 or 1/2 the cost.

[MadsMadMacMan]

I have the same problem, but with a MacBook Pro M1. 
Additionally:

- Hub works fine even though there is no actual screenimage. (although the connected Western Digital HD goes to sleep and reawakens all the time for apparently no reason. The HD is not powered via the hub, it has its own power connection)
- for a long period, screen was flawless, I don't know why. Now the problem is back. No change in setup.

BEST FIX: unplug and replug monitors power cable (Easily reachable: round cable, at the bottom of the back of the monitor)