WWI was actually the one bad time.
My family suffered a lot of boycott of the business, along with the other German-American communities in Baltimore, due to a huge prejudice from real American patriotism coming out as it would in pre-communist days. Not nearly as much during WWII. I think in just another 20 years’ time it was too exhausting to get fired up about!
Ethnic prejudice is a whimsical phenomenon, having little to do, in many cases, with real national security issues. Perhaps anti-German sentiment burned itself out in the World War I period, or maybe Germans-descended Americans were less recognizably German by the 1940s, or the Japanese issue was a distraction. Lots of factors.
George Templeton Strong, our diarist, is down on the Irish, not the Germans.