show – Macbook Professional typically makes use of incorrect 3440×1440 decision for 5120×2160 exterior monitor (TB3)

I’ve a 15″ 2019 MacBook Professional and a LG 34BK95U monitor (enterprise model of 34WK95U – identical {hardware}, longer guarantee).

The proper decision of the monitor is 5120×2160 and typically every thing works at that decision. However, typically after I join my MacBook (by way of ThunberBolt 3) or when it wakes from sleep already linked, it sends a 3440×1440 picture to the monitor, which appears to be like fuzzy and will get a warning from the monitor in regards to the incorrect decision.

When this occurs, the MacBook does not even give me the choice of utilizing the right decision in system preferences – even when I Possibility-click on Scaled, the best decision obtainable is 3840×2160. This makes me suspect it is utilizing DisplayPort 1.2 as a substitute of 1.4, as a result of I imagine that is the utmost decision DP 1.2 helps.

Generally disconnecting and reconnecting the cable fixes it, typically switching to a distinct TB3 port within the MacBook fixes it, typically rebooting the MacBook or the monitor fixes it, however nothing reliably fixes it, and typically I am going by way of all the above and nonetheless have the incorrect decision. (To reboot the monitor, I simply unplug it from the wall, wait a couple of seconds, then plug it again in.)

I primarily use the ThunderBolt 3 cable that got here with the monitor, however I additionally tried a brief passive TB3 cable – identical outcomes.

It additionally forgets the association of the show relative to my MacBook’s display screen when utilizing the incorrect decision; it remembers when it makes use of the right decision.

In 🍏 > About This Mac > System Report… > Graphics/Shows, it has the show linked to the Radeon Professional 550X with the next information:

LG HDR 5K:
  Decision:   3440 x 1440 (UWQHD - Extremely-Broad Quad HD)
  UI Seems like:    3440 x 1440 @ 60 Hz
  Framebuffer Depth:    30-Bit Coloration (ARGB2101010)
  Mirror:   Off
  On-line:   Sure
  Rotation: Supported
  Mechanically Regulate Brightness:  No
  Connection Kind:  Thunderbolt/DisplayPort

I am at present on macOS Catalina 10.15.4, however this additionally occurred on earlier variations, together with Mojave releases.

It additionally typically activates HDR mode when utilizing the incorrect decision, which simply has the impact of creating every thing a bit of darker. I believe that began with the Catalina replace.

After studying Incorrect exterior monitor decision detected, true decision not obtainable I went into the Coloration Sync Utility and Confirm discovered one difficulty, however Restore could not repair it:

Trying to find profiles...
Checking 35 profiles...
/System/Library/ColorSync/Profiles/ITU-2020.icc
   Header message digest (MD5) will not be right. 
   The file is locked. Couldn't be fastened.
Restore achieved. 0 out of 1 profiles fastened.

I additionally observed that underneath Profiles > Laptop > Shows there are 4 totally different “LG HDR 5k” entries. Unsure if that is associated or not.

After studying Exterior monitor has incorrect decision I attempted resetting the NVRAM / PRAM, however that did not repair it both.

I even have a Home windows PC linked by way of DisplayPort and it at all times works on the right decision.

Replace: It appears to be getting worse. I’ve solely been in a position to get the right decision as soon as since posting this. And it went away as quickly as the pc went to sleep.

I attempted connecting a CalDigit USB-C Professional Dock (which is definitely Thunderbolt 3, regardless of the title) after which connecting it is DisplayPort output to the monitor. The port on the dock is labeled 4k, however it may well really output the total 5120×2160 decision – however solely at 30hz. The low refresh charge is annoying however higher than the fuzziness of 3440×1440@60hz, so I am going with it for now. There have been a few instances the place I needed to disconnect and reconnect the DisplayPort cable to get any picture out, however one re-connection fastened it every time, making it much more dependable than the direct TB3 connection.

I’ve additionally ordered a generic USB-C to DisplayPort cable, so I am going to replace once more after I’ve had an opportunity to strive that.

Replace 2: USB Kind-C to DisplayPort cable behaves about the identical because the dock – right decision, however solely 30hz refresh charge.

Replace 3: I bought a maintain of a Home windows laptop computer with thunderbolt 3, and it labored completely on the primary strive, and once more after I disconnected it and reconnected it. So I believe that factors to an issue with my MacBook.

Replace 4: I now have a 2021 16-inch MacBook Professional with an M1 Professional chip. I switched the show again to DP 1.4 simply to see if it will work, however it has the identical signs because the older Intel MacBook. So, I am again to DP 1.2, which normally works.

(Sometimes the monitor will freeze after I wake the pc up, and the final time I rebooted the monitor to unfreeze it, the laptop computer crashed and rebooted as quickly because the monitor got here again on…)

Replace 5: I attempted putting in LG’s “OnScreen Management” app and underneath monitor settings, it had a software program replace “Run” button that seems to have up to date the monitor’s firmware and resolved a few of the points. I went from (3.11, 0, 2.4) to (4.12, 16, 4.17), and I used to be in a position to change again to DisplayPort 1.4 and get the right decision on the primary strive. I am going to attempt to bear in mind to submit one other replace in a couple of months.

Replace 6: No additional points since updating the monitor firmware; it has been working properly for over a 12 months now!