Brace height and ATA change (shortening brace, lengthening ATA) like that is cable/string stretch. Pretty normal for a new bow/strings to give up that ~1/8" ATA. Have you paper tuned your bow before or after? Did you measure deflection from level of a nocked arrow at brace? Have you confirmed your timing?

Since it moved horizontally, not just vertically (slowed down), that indicates you might have uneven tension in the cables side to side. Vertical drift can be a shift in your nock point with the stretch (stretch happening at one end of the string vs evenly). Did you notice any difference in the tiller balance as you broke the bow in? (Does the bow feel like it's tipping up or down more upon drawing than it did before?) Was there a difference in the ATA from one side to the other?

Love troubleshooting and tuning bows... Wish I could justify taking on a part time gig as a bowtech again...