RESOLVED : the problem is solved.
No sound randomly , after startup , sometimes ,
I use the original power supply
It is a known issue which NDSP, as always, denies. I have had it with multiple units, a friend has and there was a thread once on this forum which since then has been deleted.
I forwarded it to support multiple times as well, which has lead to nothing but their standard answer: “unfortunately we can not replicate this issue”.
On some forums this problem is described but there is no solution! Why? It is annoying for a professional musician!
I would assume it is a software related bug and therefor only solvable by NDSP. But as long as they aren’t working on it, no chance.
Btw, it’s also annoying for amateurs 
I have this same issue with my unit.
the problem is solved. 
I found a solution that solved the problem for the moment. I put WD 40 SPECIALIST CONTACT CLEANER (in French: WD 40 NETTOYANT CONTACT ) in all the inputs and outputs and power supply: it is a “dry liquid” that removes impurities and removes oxidation from electrical or electronic equipment) and everything works normally again. In summary: oxidation? dirt?
In practice I put the product in the sockets on the rear panel several times, also inserting a jack or the power supply socket with an in/out movement.
I found a solution that solved the problem for the moment. I put WD 40 SPECIALIST CONTACT CLEANER (in French: WD 40 NETTOYANT CONTACT ) in all the inputs and outputs and power supply: it is a “dry liquid” that removes impurities and removes oxidation from electrical or electronic equipment) and everything works normally again. In summary: oxidation? dirt?
In practice I put the product in the sockets on the rear panel several times, also inserting a jack or the power supply socket with an in/out movement
