main speaker - jack cable : why party up give stuttering sound?

hi and thanks for your attention.

I use a Jack cable to link my tv to my UE boom 2. sound is perfect but as soon as I try to pair the main speaker (one that is linked to the jack cable) with the party up option from app, then both speaker appaired give me a stuttering sound that turn awfull and impossible to listen.

someone has had the issue before?

would anyone have a fix for that?

thanks a lot.

rémi