I have this exact same problem in one set of our production pathtracing renders (in 5.3). It happens most frequently for me when I am rendering a square aspect ratio and an FOV of 90 (tiles for a panoramic stitch).
The way I have gotten around this problem is to overscan the render by 1%, and then crop the exr in Nuke after. The overscan can be found in MRQ under the Camera settings. One weird byproduct of this is that the exr is written with a full resolution that is 1 pixel smaller than what you set in Unreal. For example, if you set your output resolution in Unreal to be 3500x3500, it will write out a 3499x3499 image, with an expanded data window of 3518x3518.