I’m having the same problem. Old X1 box was fine. Using HDMI to the TV, then optical from TV to soundbar. I can get sound out of the TV speakers, but not through the optical. Other devices (laptop) still work fine in the same mode.
I’m wondering if the XG1v4-A outputs sound in a format my TV can’t convert for optical, but can play through its stereo speakers.
does your soundbar have an HDMI input? if so, connect the x1 set top box there and then use the HDMI out to the TV. (use the HDCP 2.2 input for 4k UHD)