[Samsung Galaxy S9  Questions & Answers] Etherealbicycle:
First of all, let me state that I am desperate. After going through many fixes and channels, I cannot find a fix. Let me also state that I am new to the forums, and apologise if I miss out anything here. Do let me know if I have missed out any important information.

The issue: When the orientation of the screen changes to landscape, the phone immediately enters the lockscreen.

Further defining the issue: This issue occurs only when the orientation of the screen changes. When screen rotation is locked and the phone is turned on its side, the screen orientation is unable to change and the issue does not occur.

Device specs:

One UI version: 2.0

Android version: 10

Baseband version: GX960FXXS8DTD1

Kernel version: 4.9.118-17633310 #1 Mon Apr 20 13:03:37 KST 2020

Build number: QP1A.190711.020.GX960FXXS8DTD1

Android security patch number:

1 Apr 2020

Timeline of issue (includes events leading up to issue and attempted fixes. Please note that I do not know what I am doing.):

9 March - Bought Galaxy S9 second hand from a phone shop, factory resetted prior to purchase. No issues watching YouTube videos or Netflix videos. Phone is kept at home and charged regularly.

? Apr: Phone settings are adjusted and a theme is downloaded. No issues still.

8 Jun 7:00am - Phone is prepared for daily use. App Inspector and ADB Debloater are used hide some apps (read: every form of Bixby) . Only system apps with a clear and unneeded function are hidden. Multiple apps are installed from the Play Store. One third party app, Ymusic, is downloaded from a website.

This app has not caused any issues on 3 other Samsung devices (S7 Edge, Note 9, S7). APK extractor is used to extract Video Editor from a Galaxy S7, and it is installed on the Galaxy S9. The S7 does not have any issues.

All apps downloaded are already present on the Galaxy S7 with no issues except for a remastered version of a game called "There Is No Game Jam Edition". The older version of the game has no caused any issues.

8 Jun 12:13pm - Two videos are watched on the YouTube app in fullscreen with no issue. Soundcloud is visited. Visited drugs.com and reddit.com. Watched more videos on YouTube app. Tested smallest possible delay in double pressing left menu button to switch between apps (like alt-tab but for Android). Discovered that while the S7 has no noticeable delay, the S9 requires more than half a second to pass after the first press in order for the second press to cause the next app in the list to be selected. If the two presses are back to back with no delay, the S9 simply stays on the app selection screen.

8 Jun 2:13pm - Watched a video on YouTube app. Turned screen to landscape, and phone locks itself.

8 Jun 2:58pm - Engaged Samsung official support in remote control session. Samsung tech used General Management in settings to reset all settings twice. Tech also removed lockdown mode from power button menu. Tech uninstalled some possible culprit apps: Ymusic, 1.1.1.1, Malwarebytes. Tech guided me to boot into safe mode. Issue persisted even in safe mode. Tech instructed me to factory reset phone. He also stated that if the issue persisted, I would have to send it to Samsung's service centers for an inspection. I expressed concern that I may have caused the glitch and that following the same setup procedure as before would simply cause the glitch to return.

Note that I also do not have access to my laptop to "debloat" , as I have sent it for servicing on the morning of 8 Jun. In addition, I have developed some sort of swollen infection on one of my fingers that makes typing into a command prompt to "debloat" not just uncomfortable but also very unhygienic (I did not see pus until this time). Writing this on a mobile device, on the other hand (or my thumbs) , is OK.

8 Jun 6:29pm - Posted this issue on Samsung Reddit and twice on corresponding Discord. Posted on Google Android help forum.No replies on all. Messaged Android enthusiast friends (who may/may not be technically competent). Friends suggested deleting One UI cache and data. Issue persists.

9 Jun 10am - Posted issue on Tech Support Reddit's live chatroom. Some members suggested posting to XDA.

9 Jun 1:34pm - Discovered that minimum delay between presses of left menu button to switch apps is now insignificant.