If you are experiencing a span longer than a few seconds on initial load of the Inbox you may want to try doing a CTRL+F5 in Chrome to clear out the local cache your browser is keeping, especially after an update.

 

For Inboxes with a reasonable amount of messages (less than 15+ GB) if scrolling to the bottom hangs and never loads it is suggested to run the Rebuild Folder function. You can do this from your system admin panel under MANAGE > DOMAINS > [...] > REBUILD FOLDER. Enter the user's email address and for the Folder Path enter the name of the folder (in most instances this will be Inbox or Boîte de Réception). Once the folder has been rebuilt it should load significantly quicker, even when scrolling to the last message.

Hopefully one or both of those will remedy the problem you are experiencing.