Can you still find the deleted emails in the 'deleted emailbox' ? let me know ok, i want to know more about this strange event

If using an imap account and you are talking about emails being deleted from either the SPAM or Trash folders please note that gmail automatically empty the Trash every 30 days and also any emails in Spam that are older than 30 days.

Are emails being deleted or do you have a filter that is being applied to the folder which is hiding the emails? Select folder and see if the Quick Filter Bar has any highlighted icons eg: the 'Show unread' icon or the 'Pin' icon ? Do you have this setting: View > Threads > All

I would also check your Account Settings > Synchronisation & Storage for gmail account make sure to select 'Don't delete any messages.'