Lights turn on at different times?
Possible reasons are: 
1) All the rows are the same brand/Type but the first two rows purchased were purchased and installed sometime in the past, maybe a year.  The third row is the same brand, but was recently purchased.  The vendor made an improvement to the driver circuit and removed the delay.  The original two had the delay, but since they came on at the same time you did not notice until the newer lights were installed.  You could test this by disconnecting the third row and see if the first two rows still has the delay.

2) the third row is a different brand, with a better circuit design that eliminated the delay start.  In reality, this is the same as #1, with the third row of lights having the latest circuit design that eliminated the delay.

I purchased three sets of ceiling lights, same brand /model on sale, and the internal circuit, driver, and placement of the driver for the LEDs were different in all three sets.  Improvement in LED lighting is constantly evolving.