"Don't wake up yet!"
The hint suggestion is tivemmoHQo' but says the correct translation is wej yIvem. When I typed in the suggested answer, it said it was wrong.
The hint system should not be viewed as "suggested answers", but rather "possible interpretations to consider as you put together the requested translation". Sometimes it will provide you with the exact phrase need, but other times it will only show you other similar phrases that cannot be used directly for the given sentence.
In this case, the phrase that the hint system showed you means, "Don't wake them up!" That's a significantly different phrase from, "Don't wake up yet," but contains many of the same words, so the software thought it would be useful. The software saw that all you needed was to drop the "them" and add in a "yet", so it thought it was giving you a close sentence that you could modify to make work here.
Unfortunately, the software has failed to realize the in Klingon, the dropping of the object "them" completely changes the prefix needed and also makes the -moH suffix unnecessary. It also failed to realize that the negative is already included in the word wej ("not yet"), so the negative -Qo' is inappropriate here.
When you ask for the hints (which you really should try to avoid doing), you will need to analyze them to see which bits are appropriate for this exercise and which bits aren't. Then rebuild the proper translation using the helpful bits.
I usually only glance at the hints because I haven't memorized a word fully yet (like vem). What does the -moH suffix mean, btw? But yeah, sometimes the green owl does indeed have a derpy moment :p He certainly shouldn't be overly relied upon for translation, much like any translation engine on the internet. qatlho'!