I discovered that TWRP v8.1t5_A14 for Mi 13 Ultra can decrypt, but at random times this is not working. As for me clearing cache and Dalvik did not help. Apps keep crashing, so I went back to previous build.
Did you try to erase all data for WhatsApp? For me this solved some issues for certain apps. Not sure about WhatsApp, that one was working fine for me.