XMR not sending/receiving not all clients

I have 10 clients on PC, tablet (surface) and one linux.

Only 3 of these machines (2 windows 1 tablet) I receive screenshot while nothing happens to the others (no error messages). I tried sending a reboot command to these 3 machines but same problem.
After rebooting one of the client it sent the screenshot, but at one point it stops responding because it is not compatible with the encoding of a video, that is another problem for another day.

Error log from CMS for windows clients :
XMDS POST ERROR CLIENT-1 GetResource Unknown error during getResource. E =

Error log from CMS for linux client :
WEB PUT ERROR /display/requestscreenshot/26 Unable to Process Queue of Player actions due to 1 of 1 player actions failed
WEB PUT ERROR /display/requestscreenshot/26 Player action connection failed. E = Cannot seal message

Some random error logs :
CONSOLE|GET|ERROR||/|Unable to Process Queue of Player actions due to 1 sur 8 actions ont échoué|
CONSOLE|GET|ERROR||/|Player action connection failed. E = Cannot seal message|

The client logs for windows do not have any error messages about this error, only “unable to get media ressource” errors that are about that other problem that is to be taken care of later.

Client, all of them as far as I am aware of, have XMR Status :
Connected to tcp://local-server-ip-of-xibo-cms:9505. Waiting for messages

The linux message has the XMR address and Heartbeat/last message = not-a-date-time

My problem is that I cannot send reboot commands to my clients and only a few send back the screenshot. I do not know why some clients work and not others as they were all configured the same way, all supposed to have v1.8 and above and the CMS is at 2.1.1