I have the same speakers, but I had zero issues about subwoofer. It connects fast and without any issues. I updated the firmware to the latest when I first set up my speakers though, maybe that’s why i had no issues. Have you checked your firmware, or updated it ? I also saw a youtube video, a guy was saying he had trouble with the power cable of subwoofer, if nothing works maybe it’s about the cable. 

I have another issue with this speaker btw, I can’t use THX and custom EQ. No matter what, Synapse 4 can’t install  THX Spatial Audio USB 1532-055A on Windows 11 Pro 24H2. Do you have a similiar issue and if you have or don’t have, what’s your system ?