Catalina gets resolution wrong when HDMI switching external monitor

1. A1706
2. LG 27UK850 has display port and HDMI 1 and 2 - Using HDMI 1
3. Running 10.15.1
4. Windows 1903
5. Dedicated 1050ti graphics card, supports display port
6. 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.

Thanks @Tesseax. I run this way because I'm too lazy to switch the monitor manually and I like the remote control of the HDMI switcher. Pity that Apple just seem to have continued backwards on external monitors since 10.14.5. My daughters MAC (on 10.14.5) shows none of these issues. Unfortunately trying to go back to Mojave yields a 10.14.6 version which has similar and worse bugs than Catalina so far. I guess I am stranded until Apple fix these issues. Thanks for the suggestion.

Well seems that 10.15.2 is out but by the initial feedback I'm thinking I may well avoid it completely give the fact that I use a external Apple 27in monitor and looks like the initial feedback is that these are now not working. There is more than 1 thread on this in mac rumors. This means I will put off playing with the MAC until the weekend because its going to need lots of stuffing around and time to determine if I am inflicted by the same issues as others and rolling back etc Appears to be a continuation of external monitor issues. Wonder if at some point Apple may get it right?

https://forums.macrumors.com/threads/external-display-not-working-since-upgrading-to-10-15-2.2215286/

Also monitors working on .1 that no longer work after .2 upgrade...

https://forums.macrumors.com/threads/external-display-not-working-since-upgrading-to-10-15-2.2215286/?post=28058184#post-28058184

Looking at the release notes there is nothing in there that I need in my daily work life other than maybe the security updates. Unfortunately they will take a back seat to workflow still being functional afterall that is what pays my bills. Anyway, weekend job to back up, test, and rollback potentially. Managing my MAC upgrades has become a hassle much worse than windows in the last 12 months.

Well had an absolute awful time upgrading to 10.15.2. Took 3 times with each rolling back to a working .1 to try again. Seems that during the upgrade process the WindowServer process dies and stops everything from progressing.

I can confirm this problem still exists in 10.15.2.

Time to roll back to avoid any other 10.15.2 issues i could inherit that I don;t want. Wasted 3.5 hrs the way it is to get an actual upgrade to work....

Well had an absolute awful time upgrading to 10.15.2. Took 3 times with each rolling back to a working .1 to try again. Seems that during the upgrade process the WindowServer process dies and stops everything from progressing.

I can confirm this problem still exists in 10.15.2.

Time to roll back to avoid any other 10.15.2 issues i could inherit that I don't want. Wasted 3.5 hrs the way it is to get an actual upgrade to work....

Well 10.15.2 kernel dumped twice overnight. Thats it rolling back to 10.15.1 as at least it did not exhibit this behaviour. Quality of these updates is getting worse in each release. Really is time to find a stable release and stick to it.

If going from Catalina back to Mojave you will get a weekly error report about potentially being hacked or some thing like that. There is a weekly validation of the firmware checksum against the release. Since Catalina updated the firmware it will not match Mojave....doesn't stop anything that I am aware of however...just another pain.

I've returned to 10.15.1. I can just manage to put up with HDMI issues but simply not the kernel crashes. At least 10.15.1 never did that to me. Guess will wait probably until the second last release of Catalina to update...that was the most stable of Mojave.

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.

Thanks @nullcode for the response I hope you do not inherit other issues. I've learn now from my past history here with Apple that once you get some thing that works stop upgrading. By the looks of it, if the external monior issues get resolve it will be almost a year after they got broken as such. Thats one slow pace to fix bugs. I'm staying on 10.15.1 for now. Thanks again for the feedback, disappointing but what was expected.