I had the same problem pooring my pool mut not that bad.
i hammered out about 5 cm of the concrete at some places with a powerdrill. the hole with the rebar jou just fill up with a strong mixture of cement and corcodile or weber waterproof tile glue 950/50..
then they rendered the poolwalls (some places 5 cm thick to get them strait.
and strait means strait in horizintal and vertical direction or you get a lot off problems with your tiling especial at/in the corners.
for tiling they used the same mixture 60/60 cement/ weber or crocodile waterproof.

my pool is 1.7 m deep 10 x 5 m and immagen NO LEAKS or cracks. so dont worry the good thing is you dont need so many tiles and water to fill it up.

when your walls are 40 cm I am sure there will be no leaks at all after fixing..