I did not just go out and buy another TV.   I didn't take a screw driver to it and investigate the electronics, solder, or capacitors.
But I did ring the firm we bought it off - records show in January  2020 - not long before Covid!    Guarantee long expired.
The sales guy said there was a LG model run out, significant price discounts available, and he had 8 in stock!
BUT he said - try this!
Go into Menu and do a complete re-set!   Just might work.
Did that, including a channel search for our area.
Results  = good!
Wife occasionally watches a 'soapy' in the afternoon - so the set was turned on at 3.30pm.  I asked her to leave it on to see if the 'freezing' occurred, as once it has come it has recurred. 
I went out to a Bible study at 7.30pm - it was going OK .
Back home  -  Still going OK at 9.45pm!
Over the last three days it 'spat the dummy' long before that!   Maybe it is cured!
I'll keep NAT informed.