viewing local htm files on Android device

I've created a simple (just text, no script) .htm file on a Windows computer ("testhtm.htm") and transferred it to my Android tablet.
In My Files - Downloads it then appears as "testhtm.htm". Tapping it and it opens with Chrome (my default browser) as "content:media/external/file/1000000383".
Long tap and select "Add to Home Screen" and an icon appears on the home screen titled "testhtm". And when tapping this it opens in Chrome.
If I now restart (reboot) the tablet and try to open the file by tapping its icon on the home page it doesn't open and I receive the message: "Chrome does not have access to the requested resource."
If I then go to My Files - Downloads I find I can open it from there. And if I then go back to the home page it will now open from there as well.
Why is this?
I have links on my home page to .htm pages located on servers on the internet which always open with no problems. But .htm files located on my tablet seem to become inaccessible from the home page after a reboot until opened from within My Files - Downloads.
Can someone with a better understanding of the Android OS than me explain what's going on?