Hot and cold usually has one of two engines, and they call for opposite responses. The first is avoidant attachment: closeness builds, their system flags it as risk, and they pull back to reset. The warmth was real and so is the retreat.
The second is plain low interest kept on a string, what dating culture calls breadcrumbing. Enough contact to keep you available, never enough to go anywhere. The cruelty of mixed signals is that these two look identical in a text thread, and your attachment style decides which one you assume.
