Is there a 3rd-party Sub (or a cable) attached to the Amp’s .LFE (Sub) port?

Yes a 3rd-party sub. Just like the front speakers. Basically the main function of an amp right?

Maybe try a different cable to the Sub and see if that resolves the issue - the Amp appears to be slow initially communicating with the Sub. Those were my first thoughts from seeing your video.

Different cable same issue tested it a few times. Different source input (internet radio, HDMI tv) also no difference. This AMP LFE sub port is meant for 3rd party subs. Seams like this menu option delay is software related.
 

Sonos Sub is to much for my livingroom. So no option for me. It would be a bad sign if wireless subs working fine and cable connected subs have a software delay issue. Sub settings are just settings. It should always be available not depending on the way it is connected. Now it’s pushing AMP users to Sonos Sub in a way. Not the reason i bought the AMP for. 

I’m pretty sure that is not going to be the case, but I’m unable to test it here, as another user like yourself, as I just use a Sonos Sub. Maybe someone else here in the community has a 3rd party Sub, with a similar setup, that can comment - it might help further, if you can perhaps state the make/model of your active Sub too. 

Thank you for your help!

I have tested it with 2 subs:

- REL Acoustics - Quake 

- Jamo - SUB 210

Sounds like a ‘bug’ if it’s happening with two different Subs and cable connections. Hope it gets resolved soon for you.