That's a shame as I have been trying to decide whether or not to pull the trigger on a 75q90r, but this seems such a fundamental flaw that I don't think I can justify spending that sort of cash on something so broken out of the box. It seems like basic functionality that every manufacturer should have no problems with - i mean pictures and sound in tandem!! Makes you wonder what sort of quality assurance is being carried out by Samsung? The lack of concern by Samsung for customers who have spent hard earned cash on flagship sets makes my blood boil. I think I am now in the position of waiting another year - LG lcd's don't look great, Sony have the retarded androidtv operating system youview etc. Maybe Samsung will resolve this issue in 2020. It's a shame as I really wanted one of these.
I feel that I should emphasise that's just my personal theory. I'm putting 2+2 together but that doesn't mean I'm right. Only Samsung's engineers will know for sure and they won't ever tell anyone.
Not that I'm recommending the Samsung Q90R here unless you're fine with their picture processing 'quirks' as documented in my earlier posts (keep in mind that 2 of the examples are with all processing options disabled too, just to avoid the mistake of thinking you can totally avoid the issues by turning off any picture processing options). But the audio sync issue is specific to having the TV pass Dolby Digital along to (certain?) audio devices via ARC if I'm understanding correctly. It doesn't affect PCM apparently and if you use Sky+HD (I can't vouch for Q as I don't have it but believe this equally applies to that also) through an AVR to the TV then you shouldn't get the issue. I don't get it anyway running through my Denon AVR, and nor do I get delay from the HD Freeview channels sending DD to my AVR via ARC (I've even just double checked that before writing this).
The main reason I'm pointing this out is that this year's Samsung Q90T model has been vastly downgraded. It's gone from hundreds of dimming zones in 2019 to this year's model having just under a hundred. Last I heard they hadn't even confirmed it'll have HDMI 2.1 yet, only confirming it for their 8K model. They're trying to push the enthusiast end of the market towards the 8K model and have effectively wiped out their 4K flagship in all but name in the process, likely hoping it'll still sell well on the brand name alone. And given I've had it confirmed that the 2018 Q9fn had all the same visual issues the Q90R has with both picture processing and local auto dimming, I wouldn't hold my breath on hoping Samsung totally revamp their picture processing (both base level and user selectable Auto Motion Plus parts).
If you can live with the many issues you'll find in this thread, are fortunate enough that your audio set up use isn't one which is susceptable to the lip sync issue, and you absolutely must have a Samsung, then I suppose it's better to jump now and beat the large downgrade that's coming.
The issue is that if you need a new TV right now and want to avoid OLED at this kind of price point in the market then there aren't really any other LED options out there. Every other company has switched to using LG OLED panels in their flagship models.
I'm stuck in this exact position in that I contacted Richer Sounds about buying an OLED and was continually advised to switch to buying the Samsung instead because they didn't feel comfortable recommending an OLED to me due to the risk of burn in/out/permanent image retention and it not being covered under both manufacturer or retailer warranties. Now, with discovering the picture issues that come as part of Samsung's package and struggling to be able to live with them, there are no other LCDs made by other companies to move to at this level and OLED has been suggested as something I should avoid.
Perhaps if you like Sony's method of motion processing (I love it personally and would've gone Sony, but the highest 2019 LCD model is lacking some features that were important in any new TV for me) and they update the 2019 model to having HDMI 2.1 with the features that brings if gaming is important to you, then that could be an option... If you don't game at all then the current model may be fine for you too. But I'd avoid any of LG's 'NanoCell' LCDs. To go LG at this point means going OLED.
[Edit: Funnily enough I've since read a report that LG are about to seriously upgrade their NanoCell LEDs for this year and so my take on them may change as of some of this year's models if they live up to what's being suggested. Thought I'd add this into this post given they'll be out within a few months.] As for the options I have given I can't wait for the new models to be released, I'm effectively stranded between sticking with a TV that has issues I just can't stop running into or potentially risking OLED at the discretion of the retailer. The TV market is currently a mess and I don't see that changing for a few years yet at least.