UK channels missing since re tune
Freeview retunes can change the frequency, power and other technical characteristics of the digital signal. This can cause problems for some receivers and not others due to differences in software, sensitivity and the quality of the signal on that cable.

Historically many TV aerials were designed to favour a narrow frequency band specific to each region. This is called a grouped aerial. If you have one of these then the retune might have pushed some channels outside of this band and the TV might be getting a weak signal for the new frequencies.

Ultimately you might need to consult a local aerial fitter who will be familiar with local issues and their solutions. This might mean changing your aerial type or adding an amplifier or filters.

Bear in mind that the problem might be temporary. Some retunes are done in two phases. You might be in an interim period with less than ideal conditions and will have another retune in a few weeks or months to implement the longer term configuration.

I suggest:


Check the antenna cable is not kinked or damaged for the best signal strength.
Check the antenna cable coax connector is wired correctly for the best signal strength. Look on the web for guides.
Perform a software update on your TV, either over the air or from the internet. In the past I fixed a severe tuning problem for someone with a receiver software update.
Some TVs let you manually enter the frequency for each channel multiplex. Check your TV's user guide and use Google to look up the frequencies you need to input for your region. After this, you might need to disable auto-retune.
You might be able to find a pattern to the channels that are missing. Look at the following website and half way down the page choose the link for your region. You should be able to find a list of frequency number changes, recommended aerial types and affected multiplexes (e.g. PSB2). Use Google to find the channels that are in each multiplex.  https://www.freeview.co.uk/corporate/platform-management/700mhz-clearance/clearance-events-2020
Check if your area is at risk of interference from mobile phone cells: https://at800.tv/im-sure-received-postcard/
Contact Samsung support.
Replace your home's TV aerial with a wideband model if your region requires it. This can be done DIY, but I would ask a professional to specify and fit it, especially if the aerial is high up on the house as is the norm in the UK.