I am aware that 意味 is "meaning" in Japanese. However, わけ while being of similar nuance seems to be a different word.
訳｛わけ｝ means 'cause' or 'reason'. 意味｛いみ｝ means 'meaning'.
Take the following sentence: 'What is the reason for this?' vs. 'What is the meaning of this?'. They are both expressing the same thought, despite using these two different words.
「わけわからない」would mean 'It doesn't make sense', but using the initial definition it could be restated as 'I don't understand the reason/reasoning.' 「意味がわからない」could carry the same meaning/reasoning, and entail a sense of confusion.