The LPC55S6x family was initial silicon die version was 0A, and this silicon was using on Revision A1 LPCXpresso55S69 boards. Revision 1B silicon has been used on Revision A2 boards. Both versions of silicon support the new, more robust debug session request method, but 1B silicon requires its use. If the correct version of IDE and/or debug probe drivers are not used then debug operation will be affected or non-functional.
When using Revision A2 boards, the current software release versions are required:
MCUXpresso IDE Version 11.0.1 or later
[Note: when using Revision A1 boards a hot fix is required for release 11.0.1. See MCUXpresso IDE v11.0.1 LPC55xx Debug Hotfix ]
Note that you may need to start from a new workspace if transitioning from one developed using a Revision A1 board to a Revision A2 board (or any target system using Revision 1B silicon).
IAR Embedded Workbench version 8.40.2 or later
Keil uVISION LPC55S6x Device Family Pack (DFP) 12.0.1 or later
J-link version 6.54c or later should be used (from the SEGGER download site). When using J-link with non-SEGGER IDEs (MCUXpresso, IAR, Keil), ensure that you IDE configuration is pointing to the latest J-Link drivers; MCUXpresso IDE 11.0.1 includes J-link drivers but these need to be updated to the latest version to support Revision A1 boards. See Updating a SEGGER J-Link installation on Windows for more information.