Cold seam

19:16 Sep 17, 2019 

As I said, I strongly suspect it is indeed company-specific jarong — and by the sound of it, not terribly appropriate, if Asker's explanation of the supposed meaning is correct.
No doubt more of the wider context would help us to understand if they are simply describing the problem, or proposing a solution (of which various options do exist).
In particualr, it may depend on whether these are direct-view LED walls, or composite LCD-type panels?

18:52 Sep 17, 2019 

for "cold seam" related to "video walls"; plenty for "seam" but none for "cold seam", nor for "hot seam" related to "video walls";

either a totally new concept, or some company specific lingo.

Cold seam - Black line that can appear between two panels - if that is the defintion, wouldn't that simply be "visible/noticeable seams"? => "raccords visibles"?

16:19 Sep 17, 2019 

https://www.actis.co.in/make-seams-gaps-video-wall-vanish
"While the use of thin bezel displays is becoming popular for video walls, the visible gap between neighbouring LCD panels can still be a problem when the viewing distances are small.

DNP recently introduced InvisiBezel to tackle this by “optically” reducing the gap to 1mm – which creates a virtually seamless viewing experience. This is an optical front cover which can be mounted on top of most popular 46” super-narrow-bezel LCD panels (from leading manufacturers such as Samsung, Toshiba, Panasonic and NEC).

The edges consist of prisms that optically stretch the pixels near the edge of the LCD panel (see image below), and has the effect of concealing the bezel/gap. As a secondary benefit, it also protects the LCD panels from damage due to scratches."