49" ultrawide monitor on my MacBook Pro often gets the proper resolution, but loses it after sleep

Hello,

I have a new LG 49WL95C curved monitor, which I connect to my MacBook Pro (Big Sur) via USB-C. I often works great and presents the proper resolution for the monitor (5120x1440). But often (not always) after sleeping, the monitor comes back at 1280x1024 and is unusable. Adjusting the display preferences usually doesn't help, as 5120x1440 is not an option, either in "display default" or "scaling" options. Rarely, the proper resolution is offered in those preferences, and selecting it works. But 90% of the time, I need to restart the MacBook Pro.

Has anyone else had this issue? Thanks in advance for any pointers or suggestions.