I managed to complete the setup by unplugging the arc from ethernet and reconnecting it again without the wire its 100% wireless now and it worked

not sure what happened as wired connection is supposed to be better no? Also never had a problem before

It may be that a reboot of the Arc cleared some fault in the OS, perhaps initially caused by a power surge. 

I have done a couple of reboots before the problem was solved. I have completely turned off the arc the sub and the surrounds and plugged them again also i have done a reboot of the router. This didn’t solve the problem if it was related to a power  surge. That should have done it no? It only worked when i unplugged the arc from ethernet and reconnect it again using only wifi.  The connection to the network then changed my rrears and sub are now connected in wm2 and the arc in wm1. I am leaning more towards a network issue but idk. 

I wish someone in sonos could take a look to the report to see what went wrong as that can help prevent any future similar issue or maybe to solve this issue for other users. I am not in a country that has a hotline for the customer service so I have only posted it here

Just to let you know guys. After a chat with sonos the issue was that the master speaker (the arc ) was disconnecting from the network. I had previously disabled wifi on the arc thinking its the logical thing to do when I am wiring it to ethernet. The sonos  representative told me that it should be kept on and turned off only if there is interferences. I have redone trueplay and it worked normally

The Sub (and surrounds) connect to all Sonos soundbars using a Wi-Fi signal generated by the soundbar. You should never turn off the Wi-Fi on a Sonos soundbar.

I didn't knew that. On many devices, you can switch off wifi when you are on a wired connection. Sometimes that can prevent the device from switching rondomly between wifi and Ethernet from time to time. I wasn't aware of how sonos handles this. Maybe they should add a line in the app " toggle off wifi only when experiencing network issues". 

I have never spent so much money on a system, with so many gaping holes in support and features!  No Android support?  For this amount of money?!  And constant issues like this lost speaker issue?  I'm an IT person and I'll be damned if I can figure out what complicated router issue they say it is.  Either the back end is poorly coded, which is most likely, or management couldn't be bothered to fix a legitimate issue like this.  I've tried everything I can think of and can't get the true play list speaker to work.  I hate Apple but was at least glad I had one of their iPads in the house to attempt to set it up.  No dice.  Thanks for nothing Sonos you really know how to help your users out 

Update:  I did not change anything, but I tried it out of desperation one final time and it worked.  Thank goodness