STM32L552RCT6 lose connecton with STM32cubeprogrammer while in BOOT mode through USB

[HTitalia]

I have a board with STM32L552RCT6 micro. I plan to update software using the usb port but I have an issue. The connection between STM32cubeprogrammer and the micro seems to be somehow instable. I can make conenction, read, write memory as expected but after some time the connection get lost. The reason is that ht RST pin of the micro goes low so the micro is reset. But there's nothing pulling down the RST pin except the micro itself. The PIN in fact is connected only to a pull-up resistor and a capacitor. So I assume the micro is pulling down the RST pin during the boot process. What's stragen is also that the time when the reset occurs is somehow randomic and it's different using different PC for programming the device.

I've checked the power supply but there's nothing strange on it. And also the data signals have a normal behaviour. I kept some oscillo waveform.
1) Vcc is going on still at around 3.3V

2) RST go down and then back up loadin the RC pullup

3 and 4) are the USB data signals

After the RST go down the connection is lost (as expected).

I can't see why the micro keep resetting.

[Tesla DeLorean]

Check Option Bytes for Watchdog being enabled.

[HTitalia]

..

[HTitalia]

The are set as shown in the image.

[HTitalia]

I've tried with the development board NUCLEO-L552ZE-Q.

Exactly the same result. The device disconnect after a while.

I’m using the latest CubeProgrammer release v2.13.0

[HTitalia]

I've tried with the development board NUCLEO-L4R5ZI.

So a different micro.

In this case the system work perfectly.

Main difference I noticed the system use different drivers:

 

Both my board and the nucleo L552ZE-Q use DFU in Fs mode

(and doen't work well) while L4R5ZI and another project we have

where we use USB for bootloading use

STM32 BOOTLOADER (and they work well).

[HTitalia]

Moreover the reset seems to came directly for the software