Update failed with `core/shipped.json is not available`

Hi,

so I finally get some time to get new version, but update failed (again :)).

1. Start updater
2. Updater failed with gateway timeout from nginx (need to tune that)
3. I push retry - it said step 7 is still running
4. I wait a while until I get endsep of 7, I pushed retry again
5. Ended here :)

Here is the log:

2017-08-15T20:09:55+0000 uilDzvyw2l [info] POST request for step "6"
2017-08-15T20:09:55+0000 uilDzvyw2l [info] startStep("6")
2017-08-15T20:09:55+0000 uilDzvyw2l [info] extractDownload()
2017-08-15T20:09:55+0000 uilDzvyw2l [info] storage location: /var/www/owncloud/data/updater-ocn0mgjslvwm/downloads/
2017-08-15T20:10:50+0000 uilDzvyw2l [info] end of extractDownload()
2017-08-15T20:10:50+0000 uilDzvyw2l [info] endStep("6")
2017-08-15T20:11:07+0000 45vb4zxvXO [info] request to updater
2017-08-15T20:11:07+0000 45vb4zxvXO [info] currentStep()
2017-08-15T20:11:07+0000 45vb4zxvXO [info] Step 6 is in state "end".
2017-08-15T20:11:07+0000 45vb4zxvXO [info] POST request for step "7"
2017-08-15T20:11:07+0000 45vb4zxvXO [info] startStep("7")
2017-08-15T20:11:07+0000 45vb4zxvXO [info] replaceEntryPoints()
2017-08-15T20:11:07+0000 45vb4zxvXO [info] replace index.php
2017-08-15T20:11:07+0000 45vb4zxvXO [info] replace status.php
2017-08-15T20:11:07+0000 45vb4zxvXO [info] replace remote.php
2017-08-15T20:11:07+0000 45vb4zxvXO [info] replace public.php
2017-08-15T20:11:07+0000 45vb4zxvXO [info] replace ocs/v1.php
2017-08-15T20:11:07+0000 45vb4zxvXO [info] replace ocs/v2.php
2017-08-15T20:11:07+0000 45vb4zxvXO [info] end of replaceEntryPoints()
2017-08-15T20:11:07+0000 45vb4zxvXO [info] endStep("7")
2017-08-15T20:11:24+0000 GZpjXPNiuX [info] request to updater
2017-08-15T20:11:24+0000 GZpjXPNiuX [info] currentStep()
2017-08-15T20:11:24+0000 GZpjXPNiuX [info] Step 7 is in state "end".
2017-08-15T20:11:24+0000 GZpjXPNiuX [info] POST request for step "8"
2017-08-15T20:11:25+0000 GZpjXPNiuX [info] startStep("8")
2017-08-15T20:11:44+0000 GZpjXPNiuX [info] deleteOldFiles()
2017-08-15T20:11:48+0000 GZpjXPNiuX [info] config sample exists
2017-08-15T20:11:48+0000 GZpjXPNiuX [info] thmes README exists
2017-08-15T20:12:57+0000 KHPcY5KwSk [info] request to updater
2017-08-15T20:12:57+0000 KHPcY5KwSk [info] currentStep()
2017-08-15T20:12:57+0000 KHPcY5KwSk [info] Step 8 is in state "start".
2017-08-15T20:13:01+0000 GZpjXPNiuX [info] end of deleteOldFiles()
2017-08-15T20:13:01+0000 GZpjXPNiuX [info] endStep("8")
2017-08-15T20:13:06+0000 hqmFdHuUot [info] request to updater
2017-08-15T20:13:06+0000 hqmFdHuUot [info] currentStep()
2017-08-15T20:13:06+0000 hqmFdHuUot [info] Step 8 is in state "end".
2017-08-15T20:13:06+0000 hqmFdHuUot [info] POST request for step "8"
2017-08-15T20:13:06+0000 hqmFdHuUot [info] startStep("8")
2017-08-15T20:13:06+0000 hqmFdHuUot [info] deleteOldFiles()
2017-08-15T20:13:06+0000 hqmFdHuUot [error] POST request failed with other exception
2017-08-15T20:13:06+0000 hqmFdHuUot [error] Exception: Exception
Message: core/shipped.json is not available
Code:0
Trace:
#0 /var/www/owncloud/updater/index.php(1138): Updater->deleteOldFiles()
#1 {main}
File:/var/www/owncloud/updater/index.php
Line:703

2017-08-15T20:13:06+0000 hqmFdHuUot [info] rollbackChanges("8")

But file is here: /owncloud/data/updater-ocn0mgjslvwm/backups/nextcloud-11.0.4.1/core.

Files in /var/www listed (don't worry about rights, it's running in docker container):

total 44
drwxr-xr-x  7 6662 6662 4096 Aug 15 22:13 .
drwxrwxr-x  3 root root 4096 Dec 11  2016 ..
drwxr-xr-x 11 6662 6662 4096 Aug 15 22:11 apps
drwxrwxr-x  2 6662 6662 4096 Aug 15 22:11 config
drwxr-xr-x  2 6662 6662 4096 Oct  4  2016 data
-rw-r--r--  1 6662 6662   57 Aug 15 22:11 index.php
-rw-r--r--  1 6662 6662   57 Aug 15 22:11 public.php
-rw-r--r--  1 6662 6662   57 Aug 15 22:11 remote.php
-rw-r--r--  1 6662 6662   57 Aug 15 22:11 status.php
drwxr-xr-x  2 6662 6662 4096 Aug 15 22:11 themes
drwxr-xr-x  2 6662 6662 4096 Mar  4 11:39 updater

Start in updater/index.php at deleteOldFiles(), around line 703, and trace how the updater resolves core/shipped.json during step 8 and rollback. Compare that lookup with the reported backup path; done means the retry path handles this state without raising the missing-file exception or rolling back the update.