Hi,
First off some logs would be good
how-to-submit-a-useful-support-request
Also with testing I found Gigabit Ethernet, caused more problems than it solved.
Also have you looked at kodi video cache.
I’m running the latest osmc with kodi v17 and these settings work well me (my videos are also on a Nas:)
<cache>
<memorysize>157286400</memorysize>
<buffermode>1</buffermode>
<readfactor>4.0</readfactor>
</cache>
Thanks Tom