You know what am I talking about, MagiskHide.
It's because that kernel has not mount namespace feature.
Finally I built a patched version of kernel 3.40 originated in Sony open source website.
I created a XDA: DEVDB project for Xperia M2 (D2302 variant) and you can find and download the boot image file.
If anyone interested in this (patching original kernel 3.40) post in this thread.
And if you want patched kernel, just give your kernel.sin file and exact model and variation of your device,then I build for you