Using Jlink Flash v8.10e, I'm not able to do anything as the software is not able to halt the core.

Looking at the code it looks the JLINK_GoIntDis function is not working.

Part of trace :
T272C 314:597.888 JLINK_GoIntDis()
T272C 314:600.768 - 2.903ms
T272C 314:600.800 JLINK_IsHalted()
T272C 314:601.216 - 0.422ms returns FALSE
T272C 314:601.280 JLINK_IsHalted()
T272C 314:601.536 - 0.260ms returns FALSE
T272C 314:601.600 JLINK_IsHalted()
T272C 314:601.888 - 0.298ms returns FALSE
T272C 314:601.952 JLINK_IsHalted()
T272C 314:602.240 - 0.302ms returns FALSE

CPU: Custom RISC-V

Regards,
Fred