Background info - I'm on a Spark unlimited VDSL plan.

A couple of weeks ago I got the new Spark Smart Modem. Everything works well apart from Fallout 76 on my PS4. Everything else works well on the PS4 - streaming, downloads, other games etc, but not Fallout 76. I can load the game but can't maintain a connection to the servers for more than 5mins.

Originally I thought it was Fallout 76, cause we all know it is full of bugs. However, this morning I discovered FO76 works fine on my old router (Spark HG630b), but still no go on the Smart modem.

I've tried turning off band steering, and I've tried putting the PS4 on its own guest network, but I am still having no luck. I checked the HG630b settings and it was all standard settings that it came with.

Is there something I'm missing in the Smart modem?