The problem you're attributing to SuperSU was due to the custom ROM you used. SuperSU is just the root manager utility, it's the ROM in question that consists of the base Android OS, and the all the drivers and other firmware that are required to interact with your phone's hardware configuration. Ideally a third-party ROM will work with all of the phone's features but that's not an absolute. Most independent ROM developers will state what works, what doesn't, and what's in progress. If things like network connectivity were sporadic, that's an indication the driver/firmware for things like the WiFi radio chip and Bluetooth chip (integral to the ROM) need to be addressed, not the SuperSU utility (which does not include networking support.)
Check the site where you obtained the ROM, there might be caveats posted there about the issues you're having. Or confirm you downloaded the correct ROM, ROMs for different models will only contain the software that corresponds directly to the intended hardware, and different models all have different components inside. A ROM for one model won't necessarily have the correct driver/firmware that will work with other models.
