「固まり切っていない」を別の言い方でいいますと、「固まり終わってない」になります。 つまり「考えがまとまっていない」状態であると言えると思います。

you check many meaning of "切る”　you already get guide line in grammarical explainning is 切る (Te form ) use as present continus meaing + いる　show the present condition form is Nagative (ないform) therefore here here shows Incompleteing stage of 切る　and then 考え　is here Idea so not object so not mean cutiing object here cames use by cut other mean Complete or finish ( exculed extrem emeragecy ) then implete unfinish came from 考え（noun)+切る（te form )+ いる　（ない from) Imcomplete idea Unfinished Idea both may be make sence in the meaning more learn in te form and need to divide cheching words