Are you certain the Sony HD recorder is in fact an HD recorder.
In the guide on the recorder the HD channels should start with BBC One HD at 101,
and then upwards.
If the recorder is only an SD model then you will not be able to view HD channels through the recorder.
As the signal to the TV is passed through the recorder then TV will get the HD channels.
If the recorder is definitely an HD recorder then try a manual retune rather than an auto retune.
Get a list of the multiplexes your nearest transmitter broadcasts online from the Freeview website.
https://www.freeview.co.uk/corporate/detailed-transmitter-information
Enter your postcode and house number and you will see list of your nearest transmitters and then a table with
a description of the multiplexes (muxes) broadcast. Each mux broadcasts several TV and radio channels.
Under the N you will see the mux number, place your cursor on the mux number and you should see a notice telling you whether that mux uses DVB-T or DVB-T2, HD channels are broadcast using DVB-T2, for me these are mux 40 and 55 (BBC B and Com 7), make a note of these mux numbers.
In the recorder Settings navigate to Manual Retune select the Channel number you want to tune.
On TVs and recorders the Channel really means the mux so select the channel number that
corresponds with the mux number.
For me I would select 40 (this is the mux for most HD channels, on my recorder (Humax Aura) I have to manually select the DVB-T2 decoder you may not have to do this with your Sony recorder., I don't with my Sony TV. If the signal strength and signal quality bars populate you are receiving HD channels, press the scan button. Repeat the process for the other HD mux number you took a note of. You may also want to retune the SD channels as well.
Having manually retuned your recorder do you now receive HD channels.
