Hi! This is a known issue and will be addressed in 5.5.1.
In the meantime you can delete %localappdata%\<ProjectName>\Saved\<ProjectName>_PCD3D_SM6.upipelinecache and run with r.ShaderPipelineCache.SaveUserCache=0 which should prevent it from happening again (note that this cvar override should removed once 5.5.1 is released).