NC 15.0.0, versions do not appear

Nextcloud version (eg, 12.0.2):
Operating system and version (eg, Ubuntu 17.04): linux (shared hosting)
Apache or nginx version (eg, Apache 2.4.25): Apache 2.4.37
PHP version (eg, 7.1): 7.2

The issue you are facing:
Using the web interface, I cannot see/restore previous versions of my files. I know they exist, since I can see them in nextcloud-data/username/files_versions folder, but when I click on “Versions” from the “details” screen of a particular file, nothing happens.

Using Firefox debugging console, I get the following message (similar in Chrome console) at the exact moment I click on “Versions”:

    **`TypeError: this.sync is not a function** core.js:2101:14
fetch    https://XXX/core/vendor/core.js:2101:14
nextPage    https://XXX/index.php/js/files_versions/merged.js:270:4
setFileInfo    https://XXX/index.php/js/files_versions/merged.js:360:5
selectTab    https://XXX/index.php/js/files/merged-index.js:9972:4
_onClickTab    https://XXX/index.php/js/files/merged-index.js:9876:4
_onClickTab self-hosted:975:17 
dispatch    https://XXX/core/vendor/core.js:3:6414
add/r.handle    https://XXX/core/vendor/core.js:3:3224

Is this the first time you’ve seen this error? (Y/N): Y, I know that versioning used to work since I have used it in the past. I do not remember if I have used it successfully after the 15.0.0 upgrade.

Steps to replicate it:

  1. Create a file
  2. Make a change so a new version is created
  3. In the web interface, click on Details -> Versions

The output of your Nextcloud log in Admin > Logging:
Nothing relevant

The output of your config.php file in /path/to/nextcloud (make sure you remove any identifiable information!):

$CONFIG = array (
  'instanceid' => 'XXX',
  'passwordsalt' => 'XXX',
  'secret' => 'XXX',
  'trusted_domains' => 
  array (
    0 => 'XXX',
  'datadirectory' => '/home/secondes/nextcloud-data',
  'overwrite.cli.url' => 'XXX',
  'dbtype' => 'mysql',
  'version' => '',
  'dbname' => 'XXX',
  'dbhost' => 'localhost',
  'dbport' => '',
  'dbtableprefix' => 'oc_',
  'dbuser' => 'XXX',
  'dbpassword' => 'XXX',
  'logtimezone' => 'UTC',
  'installed' => true,
  'memcache.local' => '\\OC\\Memcache\\APCu',
  'debug' => false,
  'updater.secret' => 'XXX',
  'maintenance' => false,
  'enable_certificate_management' => false,
  'mail_from_address' => 'nextcloud',
  'mail_smtpmode' => 'smtp',
  'mail_domain' => 'XXX',
  'theme' => '',
  'loglevel' => 2,
  '' => 'stable',
  'versions_retention_obligation' => 'auto',
  'mail_smtphost' => 'XXX',
  'mail_smtpport' => '465',
  'mail_smtpauth' => 1,
  'mail_smtpname' => 'XXX',
  'mail_smtppassword' => 'XXX',
  'mail_smtpsecure' => 'ssl',

this may be a real bug.

Better post it on githuh

Thanks for the suggestion, I filed a bug report on Github.
After a lot of tries, I finally discovered that, at least in my particular situation, disabling the Comments application breaks the versioning app as described above. Enabling again the Comments application restored the functionality as expected.
Problem solved on my side, but I would be interested in knowing whether this is a general bug or only with my configuration :confused:

EDIT: Actually, I can reproduce this on, so it seems it is a genuine bug