i got good news for you - i found a way to playback usb on the tv reliably!
i spent a couple of hours reading anything i could find on the subject then tried a few things.
the answer is two fold:
.. DO NOT use usb1 (at the side, left) - i think this drive is usb3.0, blue in color, may be too sensitive to plug ins and outs, diff hdd's, etc. use one of the other 2 at the back which looks like usb2.0 to me.
.. DO NOT use native player. use... KODI!

just install direct from playstore, version jarvis 16.0.
you can then play with video->files->sdcard; the hdd folders will show. and if u r familiar with kodi, it's easy to navigate, get subs, etc.
i tried all 3 usb drives, tried Kodi, VLC, MX, ES file explorer. Kodi is by far, the best.
i never liked using kodi for usb playback on my boxes since the native players are easier to use and superior for hd audio pass thru. so, here, i finally get to use it that way!
one more thing - don't worry about usb extension cables. i tried it, no problem. and chances are it will be required since the usb2 and 3 ports are somewhat hidden at the back.
one thing clear to me now is this sharp ue630x... while the android inside is pretty good, the usb drive/player is poor. strange they try to stinge on that. anyway, glad there is an acceptable solution.

I think tv manufacturers are moving towards the smart functions and are leaving the old USB playback via built-in media player behind. Even my Samsung JS7200's USB media player is mediocre compared to using DLNA servers and files supported is much less compared to DLNA. I guess using apps is the way to go and forget about using native players.