Audio drops from videos when playing USB 3.0 iXpand drive on iPhone 7 and on iPad Air 2

These are typically either videos i have downloaded from nanohub.org website or from iTunesU. In either case they are always .mp4 video files. I am a graduate student in a science field and try to watch vidoes on science lectrues. If you have time to try the exact videos on your iphone or ipad then here are the videos i am having issues with…

https://nanohub.org/resources/1748

at this URL, scroll down, and righ click any of the “view” items, below the Video colum, save as, and then try to play via the iXpand drive on the iphone or ipad.

video #9 in that list (9: Introduction to Metal Optics) is the one that has been giving me the most problems.

I can’t say thank you enough for all of the guidence and help thus far. I really appreicate it.