After I updated my project to UE 5.5 from 5.4, the model(shadow?) will flickring like this.
The settings of rendering and the lights have no changes.
How to fix it?
Hello there @zucchini_ue!
Considering that you have just moved to 5.5, please make sure both Unreal and Windows have their latest updates.
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As well, update your nVIDIA drivers, make sure you are picking the “Clean Installation” option, as well as going for the “Developer” drivers, as these have more stable settings for engine work.
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If your current project was on a previous version of Unreal, and its now updated to 5.5, rendering settings from the previous build could be causing a conflict. In order to reset them, please search for
DefaultGame.inifile, open it wirh a notepad, and delete all settings under the header[/Script/Engine.RendererSettings] -
To rule out hardware issues, in Unreal Engine, adjust your values for engine scalabillty, to ensure your equipment is not being exerted.
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Test disabling Hardware Raytracing from the engine
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Please make sure that no RTSS or overlocking are enabled for your video card while working on the engine.
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Additionally, there are two settings to test in nVidia control panel: Go to Settings, and under Features → Overlay, disable the “Game filters and Photo Mode” option. After that, click on “Manage 3D Settings” in the settings menu on the left, go to Monitor Technology and select “Fixed Rate”. With these changes applied, please restart UE5.
Thanks! I will have a try. 
do these work? I use 5.5 directly, export udatasmith from sketchup use plugin “datasmith”.
The mesh is also flickering
II have a very similar problem. Very flickery graphics after upgrading from 5.1 to 5.5 
Those are flickering due to moire patterns. That is repetitive patterns in geometry.
Not an expert on how to tune the rendering settings to lower this down, but you can have a look here, look at section on " TSR Flickering Temporal Analysis"
Yeah but why was this flickering not present in 5.1? And how to revert it back?