Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/Infineon/XMC1400/SCU_CLK/PWRSVCR#0x0
FPD=value1
Power Save Control Register
Flash Power Down
0 (value1): no effect
1 (value2): Flash power down when entering power save mode. Upon wake-up, CPU is able to fetch code from flash.
https://github.com/cmsis-svd/cmsis-svd-data