Cannot delete files with recognized extensions

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#1

Hi, I am trying to set up ownCloud on my CloudWays server and facing a puzzling problem. ownCloud won't let me delete files of certain types but will for others. When I try to delete image files (JPG, PNG), PDF, and archive (ZIP, TAR.GZ) files, ownCloud says "Error deleting file" at the top of the page. However, if the file is a type that ownCloud doesn't recognize, such as a plain text file without an extension or a file called "gmon.out", ownCloud will successfully delete it. I am guessing this has something to do with generating previews.

I see some errors in the Apache, nginx, and ownCloud logs, but they don't seem to be directly related to deleting files. Each time I attempt to delete a file doesn't produce another error in any log.

ownCloud is installed to a directory called "owncloud" under the web root. WordPress is installed in the web root.

From the Apache log:

[Mon Aug 29 23:07:05.073557 2016] [proxy_fcgi:error] [pid 9562] [client 127.0.0.1:39570] AH01071: Got error 'PHP message: {"reqId":"7ja\\/uNGKv1ojOJm5jZl2","remoteAddr":"127.0.0.1","app":"PHP","message":"mkdir(): Permission denied at \\/home\\/68165-53097.cloudwaysapps.com\\/wwpjyzbttf\\/public_html\\/owncloud\\/lib\\/private\\/Setup.php#288","level":3,"time":"2016-08-29T23:07:05+00:00","method":"POST","url":"\\/owncloud\\/index.php","user":"--"}\nPHP message: {"reqId":"7ja\\/uNGKv1ojOJm5jZl2","remoteAddr":"127.0.0.1","app":"PHP","message":"chmod(): No such file or directory at \\/home\\/68165-53097.cloudwaysapps.com\\/wwpjyzbttf\\/public_html\\/owncloud\\/lib\\/private\\/Log\\/Owncloud.php#114","level":3,"time":"2016-08-29T23:07:05+00:00","method":"POST","url":"\\/owncloud\\/index.php","user":"--"}\n''

From the nginx error log:
2016/08/30 00:23:42 [error] 18402#18402: *519697 open() "/home/68165-53097.cloudwaysapps.com/wwpjyzbttf/public_html/owncloud/index.php/core/preview.png" failed (20: Not a directory), client: 73.246.91.230, server: wordpress-24763-53097-139729.cloudwaysapps.com, request: "GET /owncloud/index.php/core/preview.png?file=%2Ftest.jpg&x=389&y=219&a=1&mode=cover&c=b010df27afa62f19a95b6d5c1f79f1a7&forceIcon=0 HTTP/2.0"

From owncloud.log:{"reqId":"FoOZBNjf5sAW6MDhY+Td","remoteAddr":"127.0.0.1","app":"mysql.setup","message":"Specific user creation failed: An exception occurred while executing 'SELECT user FROM mysql.user WHERE user=?' with params [\"oc_be\"]:\n\nSQLSTATE[42000]: Syntax error or access violation: 1142 SELECT command denied to user 'wwpjyzbttf'@'localhost' for table 'user'","level":3,"time":"2016-08-29T23:58:32+00:00","method":"POST","url":"\/owncloud\/index.php","user":"--"}
{"reqId":"FoOZBNjf5sAW6MDhY+Td","remoteAddr":"127.0.0.1","app":"mysql.setup","message":"Database creation failed: An exception occurred while executing 'GRANT ALL PRIVILEGES ON
wwpjyzbttf. * TO 'wwpjyzbttf'':\n\nSQLSTATE[42000]: Syntax error or access violation: 1044 Access denied for user 'wwpjyzbttf'@'localhost' to database 'wwpjyzbttf'","level":3,"time":"2016-08-29T23:58:32+00:00","method":"POST","url":"\/owncloud\/index.php","user":"--"}
The latter error is repeated several times.

Server configuration
Operating system: Debian 8.5
Web server: Apache + nginx
Database: MariaDB (also tried SQLite, but had the same issue)
PHP version: 7
ownCloud version (see ownCloud admin page): 9.1
Updated from an older ownCloud or fresh install: fresh