The two 20A radials is always an option, but if the location of the break is such that the two legs are radically different lengths, I would perhaps be focusing on fixing the problem, particularly if the circuit serves a high usage location like a kitchen.
In terms of blanking off... I would try not to remove any accessories from service... if the break is on a cable leg from one place to another, just get yourself some slim 4 way push fit Wagos and earth out the cables for that section at both ends.
In my experience, such issues have typically been caused by loose connections in the accessories themselves. Thankfully I've not had many that involved hidden junction boxes... but one of them sticks in my mind where I managed to get the location down to the wall behind a newly installed kitchen cupboard
If you don't fancy dragging the long lead around you could also just link our line and neutral on one end of the cable and then go around taking an R1+R2 reading until it goes to the dogs... then do the same but with the other leg linked out. Draw a diagram and record the results... can help working out potential cable routes and may also highlight whether you are looking for multiple issues.
Good luck