This is enabled everywhere else and recommended by the kernsec folks (https://kernsec.org/wiki/index.php/Kernel_Self_Protection_Project/Recommended_Settings). In my opinion, this can be safely enabled.
https://patchwork.ipfire.org/patch/2979/
Stackprotector was set to regular in i586-pae to ensure compatibility with paravirt virtual machines. The kernel crash with stackrotector=strong.
Okay, so I am closing this as CANTFIX.