Some evidence cannot be repeated. Some evidence cannot be measured by instruments that can be calibrated for accuracy and certainty of measurement.
But anecdotal and other sparse evidence is still evidence.
For instance, experiments in cold fusion could not be repeated easily. Sometimes they would work and frequently they wouldn't. But this didn't stop some scientists from pursuing the puzzle. They discovered, with careful measurement, why the experiments could not always be repeated. Success required the nodes to remain in a certain state perfect for the work to be done. Not all nodes could achieve or remain in this state.
Perhaps the biggest failure for scientists in the spiritual realm rests on the unwanted extra ingredient that scientists insist on using -- skepticism. If you look closely at the meaning of this word, you will find a potent bias -- doubt. Things like telekinesis, telepathy, remote viewing and the like require faith and no doubt. Scientists have been ruining their own experiments with the poor paradigm of skepticism.
Many skeptics betray their lack of logical skill by insisting that, because there is no evidence to support a thesis, the thesis must be invalid. This is an argument to ignorance type logical fallacy.
Truth doesn't care if you have evidence or not. Truth will remain Truth, whatever that is.