When I was a kid, I got really into reading the books by Stephen Ambrose. They were all about WWII, and usually from an American pov. This was before the plagiarism scandal was widely known. Now, looking back, it seems that most people are pretty heavily critical of Ambrose. He kinda rode the wave of of the patriotism that accompanied the 50th anniversary of D-day. But specifically what did he get wrong?
Plagiarism scandal? I have not heard of this.
In an old thread that was inspired by the HBO series "Band of Brothers" that was based on Stephen Ambrose's work, /u/coinsinmyrocket in this top level comment talked about some of the inaccuracies present in both the book and the show with some talk about Ambrose's methodological problems.
Later in the comment chain spawned by /u/coinsinmyrocket, /u/Bernadito linked to a particularly scathing amazon review written by Dr. Robert Forcyzk, who has some pretty decent qualifications noted in his Osprey author profile. I'd recommend reading the review, it has a good number of specific criticisms that are used to make more general points on Ambrose's Band of Brothers.
Towards the end of the comment chain, /u/coinsinmyrocket talks in greater depth on the issues of Ambrose's historical methods here and here. According to /u/coinsinmyrocket, the criticisms noted in the thread are also generally applicable to the majority of Ambrose's work.
The above mostly concerns Ambrose's Band of Brothers, so there's plenty of room for dissection and criticism of Ambrose's other works.