@kanishknishar
Hi, something on your system does this, maybe an extension.
A user report "Minimal Theme for Twitter/X" Delete user Data, for example.
I have 12 Vivaldi installs, some update several times a week, the snapshot ~weekly, I never lost history ever.
I backup my profile folder weekly, a power loss or OS crash can happen anytime and you lost data.
Maybe another user have an idea why this happen, I am out of ideas.
Cheers, mib