I have a 55" Q90R tv, model number is QE55Q90RATTXU. Like the KS8000 it replaced it has a gremlin when using the external HDD to record programmes or use the Timeshift option. The first time you use either Timeshift (TS) or Scheduled Recording (SR) it works perfectly. However, over a period of time (I've not checked but approx. 4-8 weeks) TS will not work (you get a message "Not available" or something) and although you can set up a SR, the programme will fail to record. All previously recorded programmes will continue to playback and on the face of it there appears to be nothing wrong with the external HDD and how the tv communicates with it.
Samsung support will ask you to reset the tv to factory settings, this doesn't work and you then need to re-register all of the apps (Netflix, Prime, BBC iPlayer etc.) which is a pain as this seems to be required every time you request support.
The only solution is to remove the external HDD and reformat it on a pc. When you reconnect it to the tv (the tv may also require to format it) it will work fine and normal service is resumed. However, you've lost all previous recordings unless you saved and transferred to/from pc and the fault will return again in another 4-8 weeks.
I've read somewhere that others have found the same problem and think that the tv somehow writes a bug on the HDD and the only way to remove it is to reformat. That seems plausible but you would think that Samsung engineers could easily resolve this with a software update as it seems to affect the entire range of tvs.
This is the only issue with the TV which otherwise works faultlessly and we are delighted with it. Comparing aesthetics, overall picture quality and the best operating system currently available and Samsung are our go to brand.
However, having spoken to Samsung Customer Support to try and resolve the issue it seems impossible to get through to the right person? I'm told I need to speak to someone higher up in the technical department but you have to wait for them to phone you (you cannot be put through) and upon answer of the incoming call the line hangs up! This has happened four times now in the past week.
Samsung please just fix this issue with the external HDD and I wouldn't need to speak to you!