Hi @JonasBM24, welcome to the community. I am sorry to hear about this issue. 
Try these methods one after the other. Verify whether the problem was solved after each method, before trying the next one.
- Turn off your device and then turn it back on.
- If your device has a screen protection film, make sure it's specifically intended for your Xperia™ model. It is important that such a protective film has the holes for the proximity sensor and the front camera in the correct positions.
- Make sure that there are no air bubbles, dust or moisture under the screen protection film.
- Wipe the screen with a clean and dry cloth to make sure that your touchscreen is clean.
- Make sure that Developer options is disabled. If Developer options doesn't appear in the menu, it's already disabled.
- Use the Tests feature in the Support app to carry out a quick test to check the touchscreen and display functionality. The Tests feature can assess potential hardware or software issues on your Xperia™ device.
- Restart your Xperia™ device in Safe mode. Use Safe mode to check if any downloaded applications are causing the problem. In Safe mode, your device only starts with software and applications that were already installed when you purchased your device. If the device’s performance improves in Safe mode, it’s likely that one or more of your downloaded applications are affecting the device negatively.
You can exit Safe mode and restart the device to uninstall the applications that you suspect are causing the problem. - Check if there is a software update available for your Xperia™ device using Xperia™ Companion. Tap or click here to read more about how to update and find the latest software version.
- If you can access the device menus, perform a factory data reset. Note! A reset will delete all personal content saved on the internal memory of your device. Back up data that you want to keep. Content on an external SD card is kept.
- If you can't access the device menus, perform a software repair using Xperia™ Companion. Note! All data in the internal memory is overwritten during a software repair. Content on an external SD card is kept.
- If the screen still flashes or flickers, contact us.
- Find and tap Settings > System > Developer options.
- Drag the slider beside On to the left.
- From your Home screen, tap the Application screen icon.
- Find and tap Settings > Developer options.
- Drag the slider beside On to the left.
- Find and tap Settings > System > About phone > Support. If this is the first time you start Support, tap ACCEPT to accept the privacy policy.
- On the
tab, scroll down and tap Touchscreen, and follow the on-screen instructions.
- Tap Display, and follow the on-screen instructions.
- Find and tap Settings > About phone > Support. If this is the first time you start Support, tap ACCEPT to accept the privacy policy.
- On the
- Tap Display, and follow the on-screen instructions.
- Find and tap Settings > About phone > Diagnostics.
- Swipe to the TEST tab and select a test from the list.
- Follow the instructions and tap YES or NO to confirm if the feature works.
- Tap Done.
- While the device is powered on, press and hold down the power key.
- Touch and hold Power off until the device starts to power off.
- Wait for the device to restart in Safe mode.
- While the phone is on, press and hold down the power key.
- In the pop up window, touch and hold Power off until the Reboot to safe mode message appears.
- Tap OK and let your device restart in Safe mode.
- When in Safe mode, restart the phone.
Note! To avoid permanent damage to your device, do not interrupt a factory data reset procedure.
- Back up any important data that is saved on the internal memory of your device to a memory card or other non-internal memory. If you have any encrypted files stored on an SD card, you should also remove the encryption to ensure you can still access them after the reset.
- Find and tap Settings > System > Reset.
- Tap Factory data reset > Reset phone.
- If required, draw your screen unlock pattern or enter your screen unlock password or PIN to continue.
- To confirm, tap Erase everything.
Note! To avoid permanent damage to your device, do not interrupt a factory data reset procedure.
- Back up any important data that is saved on the internal memory of your device to a memory card or other non-internal memory. If you have any encrypted files stored on an SD card, you should also remove the encryption to ensure you can still access them after the reset.
- From your Home screen, tap the Application screen icon.
- Find and tap Settings > Backup & reset > Factory data reset.
- Android 5.0/5.1: If you also want to erase data such as pictures and music, which is saved to your device's internal storage, mark the Erase internal storage checkbox (does not affect the SD card).
- Tap Reset phone/tablet or Erase everything.
- If required, draw your screen unlock pattern or enter your screen unlock password or PIN to continue.
- To confirm, tap Erase everything.
Note! Your device does not revert to an earlier software version of Android™ when you perform a factory data reset.
Performing a software repair To perform a software repair using a computer- Computer: If it is not already installed, download and install the Xperia™ Companion application from http://support.sonymobile.com/global-en/xperia-companion/.
- Open the Xperia™ Companion application.
- Under Manage your Xperia, click Software repair.
- Follow the on-screen instructions, but do not connect your Xperia™ device to the computer until you're told to in the five-step instruction in the Xperia™ Companion window.
Tip: If you can’t turn off your device, before performing a software repair, force it to shut down. To shut down, press and hold down the power key and the volume up key simultaneously until the device emits three vibrations.
I tried it also in safe mode. It still happens all the time when watching youtube, videos, viewing pics and sometimes game scenes.
I'm not the only person experiencing this. There is a discussion in reddit too. Many people are experiencing this.
Please help us.
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