It would best to upgrade the CMS and players to 1.7.9 at this point.
I don't think you want to use this date format, unless you're using international dates as well for some reason - I'd say set it to the default Y-m-d H:i
That could very well be it, please double check that IE11 is installed on all machines and the browser emulation registry key is added in the correct path on all machines.
I assume they are downloaded? (100% on status screen)
Do you have a background image on this layout? (is it .jpg format?) Is it the same with the usual forecast template without any changes to css and no background image?
You could also try to run the verify all on Modules page and restart not working clients.
Failing that you can uninstall the player, completely remove the local library and AppData xibo config files, then reinstall the player and try again.
If that also won't help, you might need to enable additional debugging on the player to see if it will log anything regarding this issue.
Since it works on most of your devices, I assume the layout itself is not a problem, while it would seem that the CMS/players versions aren't either, we would still recommend upgrade to 1.7.9 if possible.