how big (of) a problem?

Tibs wrote to me in October 2020: A few years ago, Americans started adding “ of ” in places it didn’t occur before. It gradually spread into books, and across the atlantic to here as well. I don’t have an exact timing - less than 10 years? I find it hard to remember examples, because it’s become part of the scenery, but it’s always a case where leaving out the “ of ” leaves the meaning identical…