3G/4G/LTE Base HAT with EC25 module stops soft reboot on Pi 3B+

I have a Pi 3B+ booting from USB SSD and this works 100% of the time (5 second boot delay enabled).

Either hard reboot (remove power) or soft reboot (shutdown -r now) both work as expected.

If I connect the 3G/4G/LTE Base HAT with EC25 module to the Pi and don’t plug in the USB cable, the Pi continues to function as expected.

If I connect the USB cable from the HAT to the Pi the hard reboot works as expected.

However, the soft reboot always hangs…100% of the time with no disk activity LED activity.

Has anybody come across this problem before or could shed some light on what the problem might be?