Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/STMicroelectronics/STM32L0x2/USB_FS/FNR#0x0
frame number register
FN
LSOF
LCK
RXDM
RXDP
https://github.com/cmsis-svd/cmsis-svd-data