Folder sharing link - setting expiry date

Hi,

I have a SharePoint site with a number of folders that have view only access configured at folder level for a mix of internal and external users. 

All of these links had expiry dates set on them and this has been working fine for the last couple of months. 

Today, I created a new folder and the ability to set expiry dates for the link seems to have disappeared. (I'm using the "only specific users" option when creating the link). 

Previously I would click share next to the folder name, then on the gear icon, and select a date. The option has gone. 

Not only that, but on all the previous access links I've created on all sites I can no longer see that they have an expiry date. 

There's normally a small calendar icon next to the link and that has now disappeared for all folders across all sites. 

At the moment I'm assuming this is following an update having been applied or a global setting having been changed somewhere.

I even tried creating a new, clean SharePoint site but the problem still occurs on the new site. 

Can anyone advise on what may have caused the expiry date option to disappear when creating sharing links?