Phone not shutting down properly

REPRODUCIBILITY (% or how often): 100%
BUILD ID = OS VERSION (Settings > About product): 3.4.0.24
HARDWARE (Jolla1, Tablet, XA2,…): Xperia X
UI LANGUAGE: GER
REGRESSION: (compared to previous public release: Yes, No, ?): yes

DESCRIPTION:

Since 2 weeks, everytime when I shut down my phone, I cant start it again, without doing a hard reset (power + vol up).

PRECONDITIONS:

STEPS TO REPRODUCE:

  1. Shutdown phone
  2. Screen goes black / turns off
  3. Try to start
  4. Nothing happens
  5. Reset by holding pwr + vol up
  6. phone starts

EXPECTED RESULT:

phone shutting down properly and being able to start without forced reset

ACTUAL RESULT:

not

ADDITIONAL INFORMATION:

(Please ALWAYS attach relevant data such as logs, screenshots, etc…)
Would need help to gather relevant logs here.