Not sure if it’s right to post this here as I resolved the issue, but if it helps someone…
I had a 3 column row set to equal height. The one of the column had an image that was larger than the container allowed at full width.
All browsers (including IE10) displayed it correctly. IE11 made the columns about twice the length. with empty contain. The solution was to either make the image the right size (no good as I needed to be large for other responsive views) or by adding a set width for the image with CSS. I know IE11 has some flexbox bugs, but I did not find a solution online.
Perhaps there is a better way. Makes me wonder if we need a tips area?