Please help us help you and fill where relevant:
Your LimeSurvey version: 6.0.4 230427 
Own server or LimeSurvey hosting: Own Server
Survey theme/template: bootswatch
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Hello,

I created an Array question type survey and added 5 sub-questions.
I marked the mandatory label as open.
If the user who answered the survey does not answer even 1 of the 5 questions, a warning message appears. And the 4 options that the user answered are deleted.
I noticed a problem like this after Limesurvey 6 upgrade. It was working fine in Limesurvey 5.

Many thanks in advance for your support.

Best,

Hi,
Can you update to last 6.X version and test again ?

If it don't work : report the issue
community.limesurvey.org/bug-tracker/