I have 2x 400GB cards fully loaded in both slots, and haven't experienced this before, nor indeed anyone on the 4pda forums (and trust me, they're a dedicated community). However, I do a lot of external card cleaning, so maybe there are some errors on your card. Also note that the kernel treats SD1 differently to SD2 (both custom and vanilla, the latter just doesn't use specific schedulers/scripting for it) so it may be something related to the new schedulers or script optimisation. Do this: 1) Shutdown and eject both cards. Insert them into a laptop and disk check them. Fix any errors. Incidentally - what filesystem do they use? 2) If symptoms still persist, then (and only then) try changing the SD1/SD2 scheduler algorithm, let's see if this is the issue. You'll need to have root and a kernel manager program like Adiutor or SmartPack or EX. Change the external scheduler to row/deadline/noop and see if the situation improves. 3) If symptoms still persist nonetheless, then (and only then) should you try to disable the init.d scripts. You'll need to reboot into TWRP, mount system and rename/delete the init.d folder or the 30FSTweak/40EXT4Tweak or the renice scripts. Reboot and see if the situation improves. It's highly likely that one of the 3 steps above will solve the issue.