Don’t have the M’s, so sync definitely does not drift unless grids are of.
Did you test what I asked you to check? Play a track and instant double that to another (p)layer with vinyl mode off. See if the tracks stay synced.
After that, do the same with vinyl mode on. If that drifts, the platter/spindle is the problem.
what is the pin
at least your idea works very very well, I will check tomorrow if it works thanks
Lost in translation perhaps.
The platter rests on a pin or spindle. The motor makes it all move. The SC5000M is probably a bit older already, so the grease or oil needs to be renewed.
I have the same issue with my sc live 2. It isn’t bother me much because i’m usually mixing by ear but i had a mixstream pro before and it was working perfectly.
I use your method and it works without adding grease because the mechanism runs normally, thanks again
I don’t understand what you’re saying above:
Which method works? Vinyl mode ON or OFF? Or both?
How do you know the mechanism runs normally?
If it would have worked normally, sync would not drift, while the platter spins around.
I deactivated the motorized function it works and when I then put the motorized function on it works again
So there’s no problem anymore using sync or instant double?
I don’t know why it works by doing this my cousin had the same problem and yet he used his turntable less than me
there is no longer a problem with the sync function with or without the motor function and in the event of a malfunction I will repeat your method
Well, the method is not how to solve this problem, but more how to check if a player drifts. 
I didn’t understand your sentence, you’re talking about players who drift
I’ll try one more time. Otherwise anybody care to explain in French like @DjMell26 for instance?
Your initial problem was that tracks go out of sync between two players. We call that drifting = speed not steady.
This might be because of a badly moving platter on one of the SC5000M players.
Proper way to test this, is to sync or “instant double” with vinyl mode OFF.
If sync is working with vinyl mode OFF, it would confirm that the platter or spindle pin mechanically slows down with vinyl mode ON.
One reason it suddenly works in both vinyl modes, is that the players are warm after a period of time, so the grease or oil is more lubricant.
I have never lubricated the mechanism, can you please explain to me
I don’t exactly know how to do that. There are some forum members who did. @mufasa perhaps?
Searching the forum: SC5000M - Platter issue - Engine DJ Hardware / Media Players - Engine DJ Community
Here’s his profile: