Help with frustrating HDMI sound issue please

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So I have my Sky Q HDMI out going to a manual HDMI switch, one leg goes to the TV in the front room (this works fine) the other goes via long HDMI cable to a TV in the bedroom. It's this TV in the bedroom I have a problem with. When the TV is first turned on there is picture but no sound. If I wait, after about 15 mins, the sound will come on and I'll have no problems with it until the TV is turned off.

If I disconnect the HDMI at the back of the TV and reconnect it there is instant sound.
If I plug the cable directly in to the Sky Q, taking out the switch, it works. Again instant sound when the TV is turned on.

A full power off of the TV (at the mains) doesn't help.
Changing audio formats on the Sky Q box doesn't help.
Picking 720 rather than 1080 (to reduce the bandwidth) doesn't help.

I guess this is a HDMI handshake issue but why do I have to wait 15 minutes when disconnecting the cable and reconnecting always results in the sound working.

TV is a Sharp 50FJ2K, it replaces an old LG LCD TV that worked fine until it went pop.

Any practical things I can do to fix this please?

 

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How long as is the HDMI cable?

Also don't plug and unplug things with power, even on standby

Can't remember, it's either 15 or 20M. Why never plug/unplug even on standby?

Try turning off HDMI CEC on the bedroom TV

Sorry, didn't say but I've tried turning that off and moving the cable to the non eArc port.

 

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Question: The bedroom set is 4K UHD. Is the lounge TV also 4K?

Both are 4K. I don't pay for Sky's UHD so the Sky Q's picture output is set to 1080p

Question: Is the splitter powered from the Q box HDMI socket / TV USB port, or running from its own wallwart mains transformer?

It's actually a switch I have, only one output active at time. There is no PSU.

Question: Is there a sound bar or some sound system connected to the ARC port on the lounge TV?

Neither TV has a sound bar connected. I did have the TV connecter to a Denon Amp but I've stopped using that. I'll double check I have done as I claim.

I would agree that this sounds like a HDMI handshake issue. You've done the troubleshooting to eliminate other potential problems. If I were on-site, my next course of action would be to try a splitter with EDID control so that the Q box sees both TVs as the same spec for picture and for sound.

I guess these are expensive? Could you recommend one?

A TV on its own will generally appear as a stereo audio device. One with a basic sound bar connected should present as the same. Where a sound bar can process DD then the sound will look different between the two TVs, so that will set up a bit of a conflict. In addition, the source signal from the Q box will alternate between DD and PCM depending on the channel being played and the advert breaks.

The lounge TV is a LG OLED (OLED55E6V), the last they did with 3D. They claimed the in-built sound system was like a sound bar, could it be presenting that via the EDID to cause this confusion?

 

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Thanks again @lucid that's all great info. I've managed to find the details for the switch and you're insight is spot on. It is a bidirectional device.

I see the CYP is also an amplifier which I assume should help with the long cable run to the bedroom.

 

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Following mainly the help from @lucid I've acquired a HDMI 1 in 2 out splitter. This seems to be working pretty well even with my 'unrealistically' long HDMI cable to the bedroom.

Thanks all.