Can you go Start - start to type reliability and press enter when View reliability history comes up to see if it has recorded the update fails.
If it has, click on view tech details to see if it gives an error code.
You would need to click on the red cross or info symbol for that date.
You could see if updating to 1703 will resolve the subtitles problem, but create a system image onto external media first, although you can roll back to 1607 within 10 days of updating, but the system image is a better fall back as I once had a roll back that failed to roll back.
Just click on Update now in
https://www.microsoft.com/en-gb/software-download/windows10Scroll down the page and you will see how you can create install media for 1703.
However, once you update to 1703 and go past the 10 day cooling off period, you would only be able to go back to 1607 using your system image or by doing a clean install with the 1607 disk where you would lose all of your personal stuff and any programs you have installed.
If you do create 1703 install media, then make sure you mark it as 1703.
I use DVDs with paper envelopes so that is easy to do, unlike when you use an USB.
I have my laptops set to check the DVD and USB drives before the HDD so that I can boot up with the install media to either use the restore points, restore with image or run repair cmds from the cmd prompt.
There are some changes that 1703 makes and they are that it removes Control Panel from the Start menu, but you can pin that to the taskbar by going Start - type control panel then right click on it and select Pin to taskbar.
It also changes Command Prompt to Powershell in the Start menu.
To revert that, go Start - Settings - Personalization - Taskbar and set the toggle button to Off.
It may also remove the IE icon from the taskbar - right click on the taskbar and select Task Manager - File - Run new task - type iexplore.exe into the box - check the box to run new task as an admin and press enter - you can then re-pin IE to the taskbar.
Open Windows Explorer - right click on This PC and select Properties - System Protection to ensure it is still on as some have reported that it has been turned off after updating.