The IMXRT1060RM document has the following note at the end of Table 8-2, page 196:
2. The boot ROM enables LUART1 and USB1 interrupts in
serial downloader mode, and it disables these interrupts
before jumping to user applications. However, if the boot
ROM execution is interrupted by the debug tool, it cannot
disable these interrupts; the user application needs to
disable these interrupts in the startup codes.
Please clarify "LUART1" is this really just LPUART1? LUART1 does not appear anywhere else in the document. This note does not appear in the RT1050 reference manual either.