There is a subtlety in the text as pointed out by several commentaries, see below. Apparently, the LXX recognized this and either used an older version of the Hebrew text or corrected the copyists' mistake. One form could easily be mistaken for the other text variant.
Cambridge:
I hate robbery &c.] Render with R.V. I hate robbery with iniquity, and
I will give them their recompense in truth (i.e. faithfully). Instead
of שׂלָה (= burnt-offering) we must point עו̇לָה (= iniquity). The
translation of the A.V. would shut us up to a wrong interpretation of
the prophet’s thought. The robbery to which he refers is not that
practised by Israelites on God (Malachi 3:8-9), but the iniquitous
treatment of Israel by its foes.
Ellicott
I hate robbery for burnt offering.—The Authorised Version follows the
Vulg, and Luther, but the words, commonly applied as condemning the
formal sacrifices of the wicked, do not fit in with the context, and
it is better to take the rendering of the LXX. and the Targum, I hate
robbery with violence, as referring to the spoliation which Israel had
suffered at the hands of the Chaldæans.
Pulpit
I hate robbery for burnt offering; rather, I hate robbery with
wickedness (comp. Job 5:16; Psalm 58:3; Psalm 64:7; 92:16). The
transplantation of nations was a gross abuse of the rights of
conquest. I will direct their work in truth;
Barnes
I hate robbery for burnt-offering - There has been great variety in
the interpretation of this phrase. Lowth renders it, 'Who hate rapine
and iniquity.' Noyes, 'I hate rapine and iniquity.' Jerome, as in our
translation, Et odio habens rapinam in holocausto. The Septuagint,
Μισῶν ἁρπάγματα ἐξ ἀδικίας Misōn harpagmata ech adikias -
'Hating the spoils of injustice.' The Chaldee, 'Far from before me be
deceit and violence.' The Syriac, 'I hate rapine and iniquity.' This
variety of interpretation has arisen from the different views taken of
the Hebrew בעולה be‛ôlâh. The Syriac evidently prefixed the
conjunction, ו (v), "and," instead of the preposition, ב (b), "with"
or "for"; and, perhaps, also the Septuagint so read it. But this
change, though slight, is not necessary in order to give a consistent
rendering to the passage. The connection does not necessarily lead us
to suppose that any reference would be made to 'burnt-offering,' and
to the improper manner in which such offerings were made; but the idea
is rather, that God hated rapine and sin; he hateth such acts as those
by which his people had been removed from their land, and subjected to
the evils of a long and painful captivity. And this is undoubtedly the
sense of the passage. The Hebrew word עולה ‛ôlâh, usually without
the ,ו means properly "a holocaust," or "what is made to ascend" (from
עלה ‛âlâh, to ascend) from an altar. But the word here is the
construct form for עולה ‛avı̂lâh, "evil, wickedness"; whence our word
"evil" (see Job 24:20; Psalm 107:42). And the sense here is, hate
rapine or plunder (גזל gāzēl) with iniquity;' that is, accompanied,
as it always is, with iniquity and sin. And hating that as I do, I
will vindicate my people who have been plundered in this way; and who
have been borne into captivity, accompanied with deeds of violence and
sin.
