Error after trying to enable Antivirus App for files

Steps to reproduce
1. Try to enable Antivirus App for files
2. See "App update required / These apps will be updated: Antivirus App for files (files_antivirus)"
3. Click "Start update"
4. See "Updating ownCloud to version 9.0.5, this may take a while."

Expected behaviour
The update should succeed

Actual behaviour
See "An error occurred. Please reload the page."

Server configuration
Operating system: Linux
Web server: Apache 2.4.23
Database: MySQL 10.1.17-MariaDB
PHP version: 5.6.24
ownCloud version 9.0.5
Updated from an older ownCloud or fresh install: Updated from 9.0.4.
ownCloud log: NOTE: while I used to see owncloud.log in data, there isn't one there now!

Special configuration (external storage, external authentication, reverse proxy, server-side-encryption):

Integrity status for oC9+

Can't log in, but I corrected the issues with the integrity check yesterday after updating from 9.0.4 to 9.0.5.

Q1: Is there some method by which I can cancel this app enable action to return to normal operation?

Q2: If my logs aren't being written to data/owncloud.log (and I checked my data folder location in config.php), where is it being written? I definitely saw current log messages in Admin prior to trying to enable this app!

Hi,

apps can be disabled with the occ command line tool:

https://doc.owncloud.org/server/9.1/admin_manual/configuration_server/occ_command.html#apps-commands-label

Ah, you're presuming I have shell access. I don't. Any other way?

There is also a FAQ category here having such infos:

Thanks, @RealRancor. The owncloud instance is back up and running now.

I still can't explain the absence of my data/owncloud.log file, though.