Lost user - "Could not send reset email because User does not exist."

Expected behaviour

OwnClowd should connect to the server.

Actual behaviour

OwnClowd does not connect. I tried to log through the web interface, but the password didn’t work.
After requesting a password reset I got no e-mail. Then I saw in the log this message:
“Could not send reset email because User does not exist.”

Server configuration

Operating system: Linux

Web server: Apache 2.4.38

Database: MySQL 5.5.59-cll

PHP version:5.2.17

ownCloud version:

Storage backend (external storage):

Client configuration

Client version: 2.5.4

Operating system: Win 7

OS language: EN

Qt version used by client package (Linux only, see also Settings dialog):

Client package (From ownCloud or distro) (Linux only):

Installation path of client: C:\Program Files (x86)\ownCloud

Logs

  1. Web server error log:

  2. Server logfile: ownCloud log (data/owncloud.log):
    “}
    {“reqId”:“XJS9fO-9P59NjBg81lJ09QAAABk”,“level”:3,“time”:“2019-03-22T10:48:29+00:00”,“remoteAddr”:“149.62.203.195”,“user”:”–",“app”:“core”,“method”:“POST”,“url”:"/owncloud/index.php/lostpassword/email",“message”:“Could not send reset email because User does not exist. User: admin@nestandartniizdelia.com”}
    {“reqId”:“fc875480-e79a-47d5-b46d-c0fc0aa47ba4”,“level”:2,“time”:“2019-03-22T11:48:31+00:00”,“remoteAddr”:“149.62.203.195”,“user”:"–",“app”:“core”,“method”:“PROPFIND”,“url”:"/owncloud/remote.php/webdav/",“message”:“Login failed: ‘admin’ (Remote IP: ‘149.62.203.195’)”}