Which version of Rockbox are you using? I don't have any answers, but anyone who might would need to know that. Older versions are less stable with flash mods.
If it's a micro-SD card then presumably there's a micro-SD to SD adaptor within the iFlash adaptor, which is going to add another level of possible instability, I'd have thought - be better off trying with a full size card and no adaptor. Or an iFlash quad.