Hi Schputim,
Instructions for providing logs can be found here.
Logs should tell us, why they are not playing,
When you say nfs shares are mapped is this with fstab (kernal-mount) or just adding an nfs share via kodi (software mount)? mounting via fstab would be better.
Also have you considered kodi’s video cache
reccomended settings for pi3:
<advancedsettings>
<cache>
<memorysize>157286400</memorysize>
<buffermode>1</buffermode>
<readfactor>4.0</readfactor>
</cache>
Thanks Tom.