The error you mentioned occurs when Softaculous is unable to connect your database. There could be two reasons for the same :
1. Database details are not correct in Softaculous records which can be fixed by editing the details from Edit Installation page :
https://www.softaculous.com/docs/enduser/how-to-edit-an-installation/
However as you said the details are correct this is not the issue in your case.
2. As your said your website goes down some times for a short period. It could be possible when Softaculous tried to connect to the database your sql service was not running properly.
If you still face the issue please open a support ticket with us and we will check this for you :
https://softaculous.deskuss.com/