Actually that is our mistake, we did fixed something between these version 5.2.6 - 5.2.7 regarding this email logo part, so 5.2.7 version onward is expected this /email/ without s (JoomlaFolder/templates/YourCurrentTemplate/html/com_easyblog/email/logo.png), so caused this issue.

The reason hitting this issue is because last version stored this custom logo under this path JoomlaFolder/templates/YourCurrentTemplate/html/com_easyblog/emails/logo.png (with s)

In other word, once you re-upload your custom logo from your live site under that notification setting, it should be no problem when you update next Easyblog version.

I am sorry for any inconvenience caused this recently update.