Sent items not showing in 'sent' folder

I’ve just sent a reply to an email, but it does not appear in my ‘Sent’ folder  (It does say, on the original received email ‘you replied to this message on…’)
I have tried ‘repair’ but nothing happens.
I was asked by support to attch the following screenshots…    

Sorry, the sent message has just appeared in the ‘Sent’ folder! (I don’t know why it didn’t appear there as soon as it was sent…) If anyone has advice or suggestions… I’d be grateful (will delete this post later)

Hi, I hope this was just a short network connectivity issue, let me know if the issue occurs again and we can take a further look at it.

Thank you,