Hi jovirku,
I had similar problems, but I had luck. The data are still there. The situation was as follows.
My phone is an Sony Xperia XA2 dual sim
I updated my phone without any problems. Then I created a guest account. I changed to the guest account and it worked. I went back to the owner account, I switched back again and then I tried to go back to my owner account but it doesnt work. The display was dark and nothing happend. I restarted the phone and was again in my guest account. I tried again to go back to the owner account. No chance. Then I started again, opend some apps on my guest account and tried again to go back to my owner account. Now it worked. BUT at the moment I wouldnt try this again, because its not safe. Its not clear if you can switch back from one account to another. I hope this will help you to analyze the problem.
Regards
Andreas