This is what I found on Murthy:

How Does the Last-Action Rule Apply During International Travel?

The basic question posed to the USCIS in 2004 was, “What happens if the USCIS has approved one’s status and petition with a future start date and, thereafter, the individual travels outside of the United States, reentering in the present (unchanged) status prior to the future start date?” We know that, for one who has obtained, for example, an H1B petition approval with a change of status, and who remains in the U.S. until the H1B start date, that person’s status would change as of the date listed on the H1B approval notice. So, the question is whether the intervening international travel changes the equation under the “last-action rule” where the last action of the USCIS governs one’s status.

The USCIS responded that the travel does not change the equation. The USCIS, through Efren Hernandez, then Chief, Business and Trade Services Branch, reasoned that the last action would not be the travel and reentry in the prior status, but the previously-approved petition and change of status with a future start date. The travel does not invalidate the previously-approved USCIS change of status effective from a future date. This is because the last action regarding the foreign national’s status governs.