My macbook locks screen suddenly, how can I fix the problem?

Hi farahtli.

Wondering which MacBook model you are using,

and

which MacOS version is installed on it.

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Re: My MacBook locks screen suddenly, how can I fix the problem?

Finding the cause of why this happens, may provide a solution,

... what you are doing on the Mac when the problem occurs ?

... do you get an error message that may point to the solution ?

Eg:

Check if screen time is set / runs out / or the time for using that app expires..

Apple icon (on the left, in the top menu bar) > System Preference > Screen Time

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Check how long the computer can be left idle before you are logged out.

NB: You might want to set

keyboard backlight / or the screen brightness / or the screensaver / etc.

to remind you to press a key now and then to keep from being logged out ?)

Apple icon > System Preferences > Security and Privacy > General

check if password is required (ticked) after sleep or screensaver begins.

and, if so

how long after sleep or screen saver begins is the password required ?

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OR

Are you using a particular app, when the Mac suddenly locks the screen ?

Apple support have an article online that may be helpful

If an app on your Mac stops responding, closes unexpectedly, or won’t open

https://support.apple.com/en-us/HT211916

Hope there is something here that helps you find the cause of the problem, so you can fix it.

Else feel free to post here again,

or

There is a "Get Support" link to Apple at top right on this discussion page.

All the best :-)