Tested on latest Canary #66.0.3355.0 on Samsung S7 Android 6.0.1 and not able to reproduce the issue by following the below steps: 

1. Launch Chrome with the flag #offline-pages-sharing enabled.
2. Navigate to any webpage.
3. From Chrome Settings, tap on download option.
4. Once the file is downloaded, navigate to "My Files" folder on the device.
5. From the Downloads, tap on the downloaded file.
6. Observed that Offline page is loaded successfully.

marcin@ -- Thanks for reporting this issue. Could you please let us know if we have missed anything or the issue is observed to any particular site.

Attached screen cast for reference.

Thanks in advance!

Deleted: 815303.mp4 1.9 MB

	815303.mp4 1.9 MB View Download

I'm sorry, but my replication steps were incorrect. Please use these one:

1. Launch Chrome with the flag #offline-pages-sharing enabled.
2. Navigate to any webpage.
3. From Chrome Settings, tap on download option.
4. Once the file is downloaded, navigate to "My Files" folder on the device.
5. From the Downloads, tap on the downloaded file.
6. Observe that Offline page is loaded (or user is asked about downloading again)
7. delete file from "My Files"
8. reload tab with offline page

Steps 6 - 8 sometimes need few attempts, they seems to be Android version dependent.

Thank you for providing more feedback. Adding the requester to the cc list.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

Alternative:

(1)enable flag "Enable offline pages to be shared" in chrome://flags
(2)open url: file:///storage/emulated/0/test

Tested on latest Canary #66.0.3356.0 on Samsung S7 Android 6.0.1 and not able to reproduce the issue by following the below steps provided in Comment#4.

Could you please share the screen cast of the issue for better understanding.

Thanks in advance! 

this error page can be opened in many ways (for example with steps from 6 and using non-existing url in step 2) + 

screenshot in #0 shows, that it doesn't have filename like requested.

in this situation I think, that it's 100% confirmed.

please correct me if I'm wrong.

Thank you for providing more feedback. Adding the requester to the cc list.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

marcin@ -- Request you to provide the screen cast in detail for the better understanding.

Is the issue consistently reproduced. Also, please provide the logs as well. That would help us in further triaging the issue.

Thanks in advance!

So it looks like this happens when on a Samsung, and you use the file manager (my files) to delete the file while it is open and reload the page.  Getting an error sounds expected, but the bug is that the error page could be made better by including the name of the file (that was deleted) for context.

ABoss, what would you like to see on the error page?  Just add the filename somewhere?