It could be a number of things but the usual ones are either –
1/. Field dominance – the interlaced fields may be reversed on your encoded video. This causes a stuttering effect on CRT TVs or Plasma.
fix with https://www.videohelp.com/tools/Restream.
2/. Poor standards conversion from NTSC to PAL or PAL to NTSC.
3/. Clients dirty or old DVD player
4/. DVD stock incompatibality with clients player – DVD-R, DVD-RW