Have you ever read "Meaning of Heb uncertain" in your Bible's footnotes and wondered what the problem was? After all, they gave you a translation, usually in good English. The problem is that they can't burden the text with more than a minimal notation that there is a difficulty here in the original language. They don't have space to give detailed notes on how or why they translated a certain way. I think it would be great if the English translation committees had a separate volume explaining the problems and justifying their solution. Every verse doesn't require that kind of explanation but enough do to make it interesting.
What their "meaning is uncertain" note leaves out it HOW uncertain the reading is. There are different levels of difficulty -- either we know the words but the grammar/syntax doesn't follow usual patterns so we're not sure what it means OR the words themselves are virtually incomprehensible so we give it our best shot at what it might mean.
For example, Isa 42:6 says "I have given you for a covenant (to/for/of) the peoples." The problem is that we know the words but the grammar is unexpected. Literally, we have "for a covenant people." It seems ok in English, but covenant is a noun, not an adjective, so it can't be read attributively in Hebrew. Even if that were ok, the following parallel expression in the verse is "for a light (to/for) the nations" which can't be read attributively at all. Two nouns (covenant and people) are juxtaposed without any preposition, conjunction, or even a definite article helping to determine their relationship. Context suggests the relationship is "covenant to the peoples" as is usually translated. Even so, the NRSV marks this phrase with "Meaning of Heb uncertain" because it's phrased in an unexpected way. This strikes me as odd because we still have a pretty good idea of what it says. What it means to be "a covenant to the peoples" is a problem for exegesis, not translation.
The irony is that the translations do not mark all such verses. A much more obscure verse is found in Ezek 23:42a. Literally with no attempt at making sense in English -- "And sound (of) quiet tumult with/in her and to men from the abundance of mankind being brought drunk from the desert." Again, we know what words are there, but the grammar does not yield much in the way of comprehensible meaning. It's likely there was some kind of textual corruption. For "drunken ones" the Qere wants us to read "Sabeans," a tribe of desert nomads. Not much help. The kicker is that the NRSV does not mark that verse with "meaning of Heb uncertain." I would argue that the meaning here is MORE uncertain than in Isa 42:6.
So, sometimes when that footnote is used, it's still fairly clear what the text says, and sometimes when the text is hopelessly obscure, they don't even hint at it with a note. I guess the only solution is for everyone to learn to read Hebrew.