Annoying /dev/ttyACM0 write from C issue

Hi all,

I have an STM32 connected over USB and it appears under /dev/ttyACM0.
Until now this always worked 100%, I could always read and write, I built a new image for my LIMA module and now suddenly I can no longer write to my STM32 from my C application.

However this works fine and the message is received by the STM: echo -n -e "\x02\x00\x01\x02" > /dev/ttyACM0

When I look in dmesg I do see something funny:

[ 389.334398] usb 1-1.3: new full-speed USB device number 11 using ehci-platform
[ 389.458391] cdc_acm 1-1.3:1.0: ttyACM0: USB ACM device
[ 424.476642] cdc_acm 1-1.3:1.0: failed to set dtr/rts

Do you guys know what might be after going wrong? Could some USB package that updated itself have screwed something up?