Upgrade to 1.7.8.6 failed with XML Parsing error: no element found

[Chrisbz]

Hi

I am trying to upgrade a test site from Prestashop 1.7.7.4 to 1.7.8.6
 
The 1-click-install failed so I am trying a manual install as per instructions here:
https://devdocs.prestashop.com/1.7/basics/keeping-up-to-date/upgrade/

When I ran upgrade.php I go the following error:

XML Parsing Error: no element found
Location: http://xxx...xxx/install/upgrade/upgrade.php
Line Number 221, Column 1:

^

and the last few lines of the upgrade.log are

*INFO*     v1.7.8.6    2022/06/06 - 09:45:11: Installing native module ps_facebook
*INFO*     v1.7.8.6    2022/06/06 - 09:45:11: Installing native module ps_eventbus
*INFO*     v1.7.8.6    2022/06/06 - 09:45:11: Installing native module psxmarketingwithgoogle
*INFO*     v1.7.8.6    2022/06/06 - 09:45:11: [SKIP] directory "smarty/cache" does not exist and cannot be emptied.
*INFO*     v1.7.8.6    2022/06/06 - 09:45:11: [SKIP] directory "smarty/compile" does not exist and cannot be emptied.
*INFO*     v1.7.8.6    2022/06/06 - 09:45:11: [SKIP] directory "smarty_v2/cache" does not exist and cannot be emptied.
*INFO*     v1.7.8.6    2022/06/06 - 09:45:11: [SKIP] directory "smarty_v2/compile" does not exist and cannot be emptied.
*INFO*     v1.7.8.6    2022/06/06 - 09:45:11: [SKIP] directory "/xxx...xxx/htdocs/app/cache/" does not exist and cannot be emptied.

No errors or warnings in the log file.

The admin & site appear to run OK ... so far

My questions are:

1. How do I check if the upgrade completed ?
   Or at least how much of it has completed ?

2. Where do I find the sequence of events that take place during an upgrade ?
   Reading through the upgrade.php I cant see where the smarty rebuild takes place so I am not sure where it has got to!?

3. If I need to fix something, can I then continue or re-run the upgrade or do I have to go back to backup before re-trying ?

Any help / pointers would be greatly appreciated

Thanks
Chris