I bought a second-hand house, and the landlord died less than a month after the transaction was transferred. Are there any taboos?

I don't think so. Don't think too much. The transaction transfer has not been affected, and the house has been delivered to you in advance. There is nothing to avoid. If you are always worried about these things, or you believe in them, then find Mr. Feng Shui to break them, or if you really can't get over it, then deal with the house or rent it!