HI
1. first I would suggest you refresh your LPCXPresso55s69 CMSIS-DAP firmware with LPCScrypt. Make sure your board is in DFU mode during updating. Thus we can make sure the on board debugger firmware is in good.

2. remove DFU jumper, reconnect board. you should be able to see LPC-Jlink2 appears in device manager:

then create a NEW project under a NEW workspace, test how it works. if still can't connect. test it on another computer.
3. If above can not help you, I suggest you try latest MCUxpresso IDE v11.0.1+ SDK2.6.3. I have tested these combination, it works well.
I was told SDK2.6.3 will be released on 25,Sept.
Have a great day,
Jun Zhang
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