From the context it's pretty clear Min got a viewing of Rand showing that Moiraine is important to him and he would almost certainly fail without her. That viewing was very recent (it would be interesting to compare the timeline to see what Mat and Thom were up to around the same time Min mentionned this), not something Min had been sitting on for long.

It's a dire and hopeless viewing she chose not to tell Rand about.

Then she rationalizes this by adding there'd be no point in telling Rand, and then tried to convinced herself that viewing could be wrong, justifying that notion (very half-heartedly) by mentionning that one and only one of her viewings has failed, to her knowledge (one of Moiraine's). In other words, Min is lucid and sees there's not much hope and the odds this viewing will fail are bad and yet... perhaps there's more failed ones she doesn't know about, and this one might fail too, and "almost certainly" is not "certainly" either. So she wisely kept her loss of faith to herself, and kept her mouth shut (for once. Rand really didn't need to hear "you're almost doomed to fail anyway, you needed Moiraine and she died". Even less than Min he would have concluded: well, perhaps she isn't dead, then. Out of character for him).

The viewing that failed (most likely that about Moiraine and Thom) isn't terribly important. It's largely a plot device to shake Min's self-confidence in her viewings, when she was in a situation where she could have revealed too much. Min's talent was becoming an obstacle, so Jordan undermined it a bit. Her lost of confidence was necessary, otherwise Min being Min, she would have had to pester Rand about Moiraine not being dead, because she's had a viewing of her for the future and her viewings are absolute and never fail. Jordan didn't want the plot to go this way, Rand had to suffer and keep darkening from Moiraine' death, and not get involved with any plan to save her. Jordan had to come up with something that would remind the reader (not so) subtly Moiraine isn't dead, but that would fail to convince Min she is alive. So he had Min believe all the reports, and her self-confidence in her talent undermined from it.

Earlier on, he had include a first major "wrench" in the prophecies, by having the Finns reveal that it is possible to step outside the paths of "fate" (as Fain apparently managed to do) and to die. The prophecies then became something that will happen... if no one involved side-steps fate.

He went another step later on, and announced that Min's new viewings (and new dreams and foretellings) aren't certain like the older ones. What's set to happen is still set to happen, but the Wheel has lost some of its control over what remains to be woven of the future. That's a plot device so that prophecies are uncertain now. They no longer foreshadow only, they can turn into pure red herrings. Jordan's oracular talents in WOT were extremely useful to him earlier on, but toward the end, having increased and multiplied, he had to give a random/uncertain aspect to them or he'd be forced to stop using them as they would be too revealing at this point.

Now he can pepper the finale with new "prophecies" that could be right, only partly right, or turn out wrong, and twist our expectations. It's prophecies fitting for the third act, alonside the most obscure of the early ones (Sheriam's aura, Rand as a beggar and so on) that are now being fulfilled at last, while many of the more obvious are behind us by now.