The "use device/phone MAC address"-option does not work

Hi there,
when I choose the option to not randomize my WiFi-MAC-address and to use the device’s MAC instead, this has no effect and the MAC is going to be randomized again on next startup of teh device. Moreover also the device’s MAC ( which you can find in the device information ) is changed and set to WiFi-MAC. - Is this a bug or depending of the the device? Searching the net I found only very few cases like this and the solutions presented there did not work for me ( developer options … ). Would appreciate if anybody had an idea which helps. Thank you in advance!

My environment:
Device: Gigaset GS290 - selfinstalled via adb
/e/OS: 1.14 R
boot.img rooted with magisk.
Developer option ‘Persistent randomization’ set ( Switch = off ).