Anime Spoiler
The "First time" he lost his power was in the fight vs Reiji & Byakuya where his Zanpakutō broke. (he didnt lost the powers just his Zanpakutō) he fixed that by learning the name of his Zanpakutō and actived the shikai form
The next time he lose his power is in the fight vs Aizen-sama where he had to use Saigo no Getsuga Tenshō which had the drawback to that he loses his shinigami powers (but he had little bit Spiritual Power left inside)
Instead of shinigami powers he learns how to use fullbring from Kūgo who later steals his fullbring power.
After he lost his new fullbring Rukia stabs him with a Sword made out of the Spiritual Power of the Gotei 13´s senior officers to reactive his Spiritual Powers.
Manga Spoiler from the last Arc
next time he loses his power is because Jugram Haschwalth broke Ichigos Bankai Zanpakutō.
He learns from Mayuri that a Broken Bankai cant be fixed. after that the Royal Guard took him to the Soul King Palace in order to reforge his Zanpakutō.
then he got his dual Zanpakutō (which had both of his powers inside | Quincy / Shinigami)
the last time he loses his power in the fight vs Yhwach but Orihime restored his power with her power
i hope its readable xD english is not my native language ^^