User issues

Following a recent vacation I wanted to share photos so went through the following steps.

Created a share to a folder full of photos
Set up user accounts with username and email address
tested the user setup and share with one of my own email addresses - it worked.
so far so good…

I then found that some users could connect straight away, others either had to try multiple times or simply, either never received the notification email, or having received the email, couldn’t then connect.
Has anyone seen this type of issue and then found a resolution?
I have removed users and recreated them, sometimes this worked other times it hasn’t worked.

Second point - Is it possible to see which users have logged on and when they logged on?