Please open "Settings - Video Configuration - Video Orientation". If you plan to record games or other apps with landscape screen, please set Video orientation to Landscape.
If you select "Auto orientation", the orientation of recorded video will depend on screen orientation at the moment of start recording.

If you cannot open recorded video with any media player, that means recorded video is corrupted. The most common reason is system killed the record-service. While recording the record-service runs in background and has lower priority than other apps, which run foreground. Screen recording is a heavy task and requires a lot of resources. Therefore sometimes your system must kill the record-service for saving memory, battery and other resources for higher priority apps. We recommend to reduce the resolution, bitrate and length of video for more stable recording.

Google doesn't provide API for recording internal audio on Android 5.0 or higher. Therefore currently Screen Recorder only supports recording sound via microphone

Google doesn't allow to access microphone in parallel. That means the Video call app and Screen Recorder can not record sound at same time!

If you try to record a movie of an entertainment app (like Netflix, Telly, OSN Play…), you might get a blank video with audio only.
It is the copy right issue.These apps can prevent users from screen recording to protect their content.

It seems to be a problem of your ROM. Somehow the screencast feature doesn't work. You should contact the manufacturer to report this issue.

On Android 5.1, you will get "System UI Crash" if you select "Don't show again" in the capture permission dialog.
It is a problem of Android 5.1. Therefore the only way to solve it is reinstall Screen Recorder and remember to "not select Don't show again" in the capture permission dialog.

Please check the type of setting you selected

While recording the record-service runs in background and has lower priority than other apps, which run foreground.
Screen recording is a heavy task and requires a lot of resources. Therefore sometimes your system must kill the record-service for saving memory, battery and other resources for higher priority apps.
We recommend to reduce the resolution, bitrate and length of video for more stable recording.

If you enabled "Show touches" in Screen Recorder, it will work after opening app and stop working after exit app. you can disable it by going to Developer Options in Settings of your phone

On some Xiaomi, Meizu… devices "POP-UP WINDOW" is disabled by default. Therefore the some option of Screen Recorder cannot be shown.
Please open AppInfo of Screen Recorder and grant the "POP-UP WINDOW (Alert) permisson"