The Wall Street Journal doesn't always write very clearly. Some authors are particularly verbose and confusing ;)
For example, "More uncertainty is unwelcome" is just poorly written because it is a double-negative. I don't know how this logic applies to Russian, but usually in English, a double-negative turns into a positive:
"More uncertainty is unwelcome" = "More certainty is welcome" = "People desire and hope for more certainty and clarity"
It's basically saying that, even though right now, Trump's tweets are not asking for immediate changes to how supply chains are structured and trade policy is organized, no one knows what might happen tomorrow or next week because he changes his mind often. And everyone fears that he might introduce more uncertainty tomorrow or next week, and they do not welcome this potential uncertainty.
"While Mr. Trump’s tweets are unlikely to trigger immediate changes, more uncertainty is unwelcome." = "Even though Trump's tweets are not causing any immediate changes to supply chain structures and trade policies, no one knows what will happen tomorrow, and everyone fears more uncertainty / sudden changes from upcoming tweets."