Problems with Marantz and Firestick 4K

Good evening,

My name is Miguel Ángel, and I’d like to share a problem I’m experiencing where I feel a bit lost.

I have a Marantz AV 7013 with dual monitor outputs, a Raspberry Pi 3, and LED control via PWM. The connection to my Panasonic TV is through one of the two HDMI monitor outputs on the Marantz.

Marantz

--> Monitor 1 (ARC) directly to the TV

--> Monitor 2 to the input of the Raspberry Pi capture card.

Additionally, I have several devices connected to the Marantz: PS5, Blu-ray player, Nintendo Switch, and Firestick 4K. All the inputs work perfectly, except for the Firestick. However, if I connect the Firestick to an external splitter, it works fine.

Does anyone have any idea what could be causing the issue?

I try to test.

Thanks a lot.

Any splitter preference?

Thanks!!

Ambientheater77, any splitter with ARC also?

Thanks a lot!!