Having two Xperia XAs suffering with similar problems i followed the advice given here (/t5/Xperia-XA-XA-Ultra/Xperia-xa-internal-memory-running-low/td-p/1212272#gref).
At the first stage, the phone refused to transfer the apps over to my 128Gb microSD, instead rebooted itself.
I tried stage 2, the phone started calculating where all the data is being used. Phone has not responded since, and i can't even turn it off and on again...
