Manomaya Kaya (Gandhabba)

A human existence (bhava) could last hundreds or even thousands of years. Many human births (jāti) can occur during that time

In rebirth stories, there is always a “time gap” (typically several years) between successive human births (jāti). Between those successive lives, that lifestream lives as a gandhabba without a physical body.

Even during a given human life (jāti), the gandhabba may come out of the physical body under certain conditions; Out-of-Body Experience (OBE)

The human bhava is hard to attain. However, there can be many births within a given human bhava until the kammic energy for that human bhava runs out. Otherwise, how can one explain all these rebirth accounts, where a human is reborn only a few years after dying in the previous human life?

https://puredhamma.net/living-dhamma/mental-body-gandhabba/

Kamma-vipāka (Pali: intentional action and its consequence) is the Buddhist moral law of cause and effect. Kamma refers to any intentional volitional action (through body, speech, or mind), while vipāka is the ripening, fruit, or result of that action.

All living beings are born with a “mental body” (called “trija kāya” or three bodies) consisting of the kammaja kāya, cittaja kāya, and utuja kāya.

1. kammaja kāya refers to the subtle, mental body (or "karmic body") generated by past kammic energy, which carries one's life stream and karmic blueprint across different existences. It serves as the foundation that directs physical rebirth.
2. cittaja kāya translates to the "mind-born body" or the continuous stream of thoughts and consciousness. It is a core concept in Buddhist psychology and phenomenology used to describe how mental phenomena assemble and form our moment-to-moment experience of the world.
3. "utuja kāya" translates to "body born of heat" or "temperature-born body".

Connection to the "Gandhabba": The utuja kāya combines with the kammaja and cittaja kāyas to form the energetic blueprint of a being, often referred to in Pali as the manomaya kāya or gandhabba (the subtle "mind-made" body that survives death and seeks a new womb for rebirth).

This trija kāya in human and animal realms is given a unique name, “gandhabba.” It is well-shielded by the dense physical body. Thus, even an ānantarika kamma can not bring vipāka until the death of the physical body.

Mahānidānasutta (DN 15)

“.With consciousness as a condition, there is mentality-materiality (nāmarūpa). How that is so, Ānanda, should be understood in this way: If viññāṇa were not to descend into the mother’s womb, would mentality-materiality (nama rūpa) take shape in the womb?” “Certainly not, venerable sir.” “If the descended viññāṇa were to depart, would mentality-materiality be generated into this present state of being?” “Certainly not, venerable sir.”

• Here, it is clear that by “a viññāṇa descending to the womb,” the Buddha meant the descent of the manōmaya kaya (gandhabba), not the paṭisandhi citta. A paṭisandhi viññāṇa cannot come out (depart) of the womb! 
• A gandhabba has all five khandhas.
• The Pāli word “Okkanti” is often mistranslated as “rebirth.” But it means the “descend” of an already formed manōmaya kaya (gandhabba). Rebirth happens (and a gandhabba is born) within a thought moment, at the cuti-paṭisandhi moment.

Paṭisandhi (“paṭi” is to “bind,” and “sandhi” is a “joint” in Pāli or Sinhala.) Thus, paṭisandhi means joining a new life at the end of the old. That happens a thought-moment after the last citta of the current existence (bhava.)

Old kamma bring vipāka with various ārammaṇa. Mind gets attached to such ārammaṇa and engage in more kamma. That is why the rebirth cycle never ends, UNTIL one fully grasps that process and takes steps to stop attaching to such ārammaṇa.