@youarereading "leaving it in rice for a few days, it was working perfectly fine. " Nope! It is not fine. While you let it sit in rice, corrosion set in, residue seeped under components and was left behind while water around it evaporated. This creates short circuits and components will fail. '''Rice does not work!''' It does not do anything. It does not repair your device nor does it prevent corrosion.
You need to try to resurrect your phone if you are wanting to fix it. For that, you will have to totally disassemble it. Use [[Topic:OnePlus X|these guides]] to at least get into it. [https://www.youtube.com/watch?v=bNUiF12Gc-s|This video] will also help you. Once open, clean it with a soft brush and 90%+ isopropyl alcohol. Use [guide|5825|this guide] for the cleaning. Even so it was written for an Apple iPhone, all the steps are still pertinent to your phone as well. Remove all EMI shields of your motherboard to clean it properly.
Once it is cleaned reassemble it and '''replace''' the battery. This is a must since it will fail. Then check your One Plus X for proper function. If you do not take care of the water damage you cannot properly troubleshoot your damage.