Catalina gets resolution wrong when HDMI switching external monitor

I've been using my MAC with a HDMI splitter to share a 4K monitor for a number of years. I've ever had a issue until the last 2 supplementary release of 10.14.6 Mojave where it seems resolution and control of the monitors got all mixed up (see my previous posts). The fix to Mojave night shift resulting in high cpu (as the kernel tried to change resolution every 1ms) was to upgrade to Caalina or turn off night shift. Indeed Catalina did fix the kernel issue however now with Catalina I have a separate issue. Normally the 4k monitor runs at 60hz and 3840x2160. However, with Catalina, if I switch the monitor between the MAC and windows and then back to MAC when reconnecting to the MAC it selects 30Hz and a resolution that is much lower than before switching and large fonts. The only way to get the resolution back is to completely disconnect the MAC, wait 30 seconds, and then plug it back in. Kind of defeats the purpose of HDMI switching but.... This particular issue did not happen with Mojave or High Sierra so it appears Catalina specific. Anyone aware of any settings that could address this behaviour?

MacBook Pro 13", macOS 10.15

Posted on Dec 1, 2019 11:24 AM

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20 replies

nullcode

Level 1

13 points

Jan 25, 2020 7:12 PM in response to BradSP

I would like to know too. This issue is getting old fast :P

BradSP Author

Level 1

75 points

Jan 29, 2020 11:44 PM in response to nullcode

Well 10.15.3 is out but looking at all the horror stories I don't think I am going to even attempt an upgrade. Would appreciate if some other brave person could provide some feedback.

BradSP Author

Level 1

75 points

Dec 1, 2019 1:04 PM in response to Tesserax

A1706
LG 27UK850 has display port and HDMI 1 and 2 - Using HDMI 1
Running 10.15.1
Windows 1903
Dedicated 1050ti graphics card, supports display port
Simplecom CM324 splitter

I have a bootable backup of Mojave 10.14.6 sup 2 (think its G103 form memory) prior to upgrading to Catalina. If I boot the MAC off that this problem does not exist. The hardware remains the same bar the OS and the Boot Drive. The issue only occurs if I boot Catalina and use the internal SSD to boot from.

Tesserax

Level 10

157,860 points

Dec 1, 2019 4:53 PM in response to BradSP

Thanks for the additional information. Is there any reason that you are using the HDMI splitter and not just connecting a second HDMI cable from the PC to the monitor's second HDMI port? ... or using a direct DisplayPort-to-DisplayPort connection between this PC and the monitor?

FWIW, I have a somewhat similar setup at you. In my case I have a Dell 4K monitor that has HDMI, Mini-DisplayPort, and a DisplayPort ports. My home-built PC, is also running Windows 10 1903 and has an EVGA 980 card. I have the PC connected via DisplayPort and my 2018 Mac mini by HDMI to this monitor. Works great. However, it didn't originally when I first upgraded to macOS Catalina. I had to use a USB-C-to-HDMI adapter on the mini to get the HDMI connection to be consistent as it was exhibiting the same resolution problems you are getting. However, after upgrading to 10.15.1, I was able to return to using a straight HDMI-to-HDMI connection without any resolution issues. Switching the display between computers is done via a front panel controls on the monitor itself.

BradSP Author

Level 1

75 points

Dec 26, 2019 12:36 PM in response to nullcode

Well, as I know 10.14.6 is buggy, and there is no way to get to 10.14.5 that I am aware of, and since I'm on holidays and have the time addressing apple MAC OS instability issues, I rolled one of my 3 household MACs backwards from Catalina to High Sierra. This issue, the issue regarding polling external monitors when asleep, and the internal display brightness being maximum when connecting an external monitor have have disappeared. I'm in the process of intstalling my work applcatin back to the machine. Decided to use it for work with a 2 generation old OS because it works much better than the other options. Sadly I could not figure out how to get to 10.14.5. I don't think its possible unfortunately. However HS is working for me just a pity that the stablity for external monitors has been lost since then.

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Catalina gets resolution wrong when HDMI switching external monitor