Topic: Elgato + NES clone (Retro-Bit RES Plus HD): Strange issue (audio async)

Maybe you guys can help me. I contacted Retro-Bit and asked on the Elgato subreddit, but got no answers.

I own a Retro-Bit RES Plus HD (PAL) and want to stream NES gameplay (I'm a retro game streamer).

I own a Elgato HD60 PRO capture card and stream a lot of different game consoles like original SNES, Xbox one, PS2, Wii without issues.

When I plug the Retro-Bit clone in my Elgato to stream, after like 20 minutes the sound is 2 seconds behind the video. This only happens with the RES Plus and is only noticable when I plug it in my Elgato,

When I plug the RES Plus directly into my TV, everything is fine. No other console I own (PAL or NTSC) has this kind of issue. I tried setting the FPS of the capture device to 50 fps without changes.

Have you guys an idea what could cause this? I think it's pretty strange because it only happens with the RES Plus.

Thanks in advance!