Here are a few things to think about. Perhaps some of you can add to these.

1) Similarity is not identity!

Because you had a previous system with similar symptoms and found and fixed the problem does not mean the next system with similar symptoms has the same cause. That is operating on the assumption that similarity is identity. That is not troubleshooting.

2) Symptoms are not the cause!

Don't confuse the symptoms of the cause with the cause of the symptoms. Treating the symptoms may make one or more of the symptoms go away but it does not remove the problem. In fact, it probably inserts yet another problem and the whole problem is compounded. Know the difference between symptoms and the cause of the symptoms. Some doctors treat the symptoms instead of finding the cause. We need to be better than that.

Got any more?