Are you holding SW1 during boot? As you mentioned it should enter MSD mode by doing this. Could you please explain what is the behavior you are seeing on your side?
I have been experiencing the same issue with my board. At first I could detect it as MSD when long press SW1. Then I tried to flash boot loader and bootstrap program to hyperflash. (These are sample codes given with SLN-VIZN-IOT SDK). After that I can't enter MSD mode using SW1. Hardware is still working, because there is no problem in running other programs both in RAM and hyperflash. Could you please give an immediate assistance.
(I am using SLN-VIZNAS-IOT board, MCUXpresso IDE and sdk_2.x_SLN-VIZN-IOT version 2.5)