HTTP error on upload followed by disappearing assets weirdness.

A client reported getting HTTP errors when he attempted to upload images to his gallery. The problem seemed to resolve itself, but he then reported that about a third of his images had disappeared from his assets pane. I think it's a client side problem but just wanted to check if you've heard of this kind of thing happening elsewhere.

Perch: 2.8.7
Production mode: Production (100)
Installed apps: content (2.8.7), assets (2.8.7), categories (2.8.7), perch_blog (4.6), perch_forms (1.8.3), perch_gallery (2.8.6), perch_kraken (1.0), perch_backup (1.2)
DB driver: MySQLi
DB tables: perch2_blog_authors, perch2_blog_comments, perch2_blog_index, perch2_blog_posts, perch2_blog_posts_to_tags, perch2_blog_sections, perch2_blog_tags, perch2_blogs, perch2_categories, perch2_category_counts, perch2_category_sets, perch2_content_index, perch2_content_items, perch2_content_regions, perch2_forms, perch2_forms_responses, perch2_gallery_albums, perch2_gallery_image_versions, perch2_gallery_images, perch2_kraken_jobs, perch2_navigation, perch2_navigation_pages, perch2_page_templates, perch2_pages, perch2_resource_log, perch2_resource_tags, perch2_resources, perch2_resources_to_tags, perch2_settings, perch2_user_privileges, perch2_user_role_privileges, perch2_user_roles, perch2_users
Users: 4
App runtimes:
<?php
    $apps_list = array(
        'content', 
        'categories',
        'perch_gallery',
        'perch_blog',
        'perch_forms',
    );
Scheduled tasks for perch_blog: delete_spam_comments (1440 mins)
Editor plug-ins: ckeditor, tinymce, redactor, markitup
H1: cd0260c4f4f0bb537c4f9c23a38f224c
L1: 58171556e8cc89b5374107af83086924
headerColour: #ff8000
content_singlePageEdit: 1
helpURL:
siteURL: /
hideBranding: 1
content_collapseList: 0
lang: en-gb
update_2.7.10: done
on_sale_version: 2.8.26
perch_gallery_update: 2.8.5
update_2.8.2: done
perch_blog_post_url: /blog/post.php?s={postSlug}
update_2.8.4: done
headerScheme: dark
perch_gallery_bucket_mode: single
perch_gallery_bucket: default
perch_blog_slug_format: %Y-%m-%d-{postTitle}
perch_blog_akismet_key:
perch_blog_max_spam_days: 0
perch_backup_mysqldump_path:
dashboard: 1
hide_pwd_reset: 0
content_hideNonEditableRegions: 1
content_frontend_edit: 0
perch_gallery_basicUpload: 0
perch_blog_comment_notify: 0
update_2.8.6: done
update_2.8.7: done
perch_kraken_api_key: e1d821f52f0312d2a50e7b3c32ba3860
perch_kraken_api_secret: beff497397153a06440ea09b2116737ca5e536e3
perch_kraken_url: https://longshot.photo/
perch_kraken_dev_mode:
latest_version: 2.8.15
update_2.8.18: done
logoPath: /perch/resources/secular-badge.jpg
perch_blog_update: 5.0
PERCH_DEVELOPMENT: 10
PERCH_STAGING: 50
PERCH_PRODUCTION: 100
PERCH_DB_USERNAME: longshot_perch
PERCH_DB_SERVER: localhost
PERCH_DB_DATABASE: longshot_perch
PERCH_DB_PREFIX: perch2_
PERCH_TZ: Europe/London
PERCH_EMAIL_FROM: markrphoenix@gmail.com
PERCH_EMAIL_FROM_NAME: Mark Phoenix
PERCH_LOGINPATH: /perch
PERCH_PATH: /home/longshot/public_html/perch
PERCH_CORE: /home/longshot/public_html/perch/core
PERCH_RESFILEPATH: /home/longshot/public_html/perch/resources
PERCH_RESPATH: /perch/resources
PERCH_HTML5: 1
PERCH_RUNWAY:
PERCH_ERROR_MODE: DIE
PERCH_DATE_LONG: %d %B %Y
PERCH_DATE_SHORT: %d %b %Y
PERCH_TIME_SHORT: %H:%M
PERCH_TIME_LONG: %H:%M:%S
PERCH_DEBUG:
PERCH_PREVIEW_ARG: preview
PERCH_TEMPLATE_PATH: /home/longshot/public_html/perch/templates
PERCH_DEFAULT_DOC: index.php
PERCH_DEFAULT_EXT: .php
PERCH_PRODUCTION_MODE: 100
PERCH_RWD:
PERCH_HTML_ENTITIES:
PERCH_SSL:
PERCH_STRIPSLASHES:
PERCH_PROGRESSIVE_FLUSH: 1
PERCH_AUTH_PLUGIN:
PERCH_DB_CHARSET:
PERCH_DB_PORT:
PERCH_DB_SOCKET:
PERCH_APPS_EDITOR_PLUGIN: markitup
PERCH_APPS_EDITOR_MARKUP_LANGUAGE: textile
HOSTING SETTINGS

PHP: 5.5.30
Zend: 2.5.0
OS: Linux
SAPI: cgi-fcgi
Safe mode: not detected
MySQL client: 5.5.45
MySQL server: 5.5.48-cll
Extensions: Core, date, ereg, libxml, openssl, pcre, sqlite3, zlib, bcmath, calendar, ctype, curl, dom, filter, ftp, gd, hash, iconv, SPL, json, mcrypt, mysql, mysqli, session, standard, posix, Reflection, Phar, SimpleXML, sockets, imap, tokenizer, xml, xmlreader, xmlwriter, cgi-fcgi
GD: Yes
ImageMagick: No
PHP max upload size: 8M
PHP max form post size: 8M
PHP memory limit: 64M
Total max uploadable file size: 8M
Resource folder writeable: Yes
Session timeout: 24 minutes
Native JSON: Yes
Filter functions: Yes
Transliteration functions: No
AUTH_TYPE: Basic
DOCUMENT_ROOT: /home/longshot/public_html
GATEWAY_INTERFACE: CGI/1.1
HTTP_ACCEPT: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
HTTP_ACCEPT_ENCODING: gzip, deflate, sdch
HTTP_ACCEPT_LANGUAGE: en,en-GB;q=0.8
HTTP_CONNECTION: keep-alive
HTTP_COOKIE: cmsa=1; PHPSESSID=9778d2bef15ff17684b8e0c00df09fdb; _ga=GA1.2.1380617805.1456144634; _gat=1
HTTP_HOST: longshot.photo
HTTP_REFERER: https://longshot.photo/perch/core/settings/diagnostics/
HTTP_UPGRADE_INSECURE_REQUESTS: 1
HTTP_USER_AGENT: Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/48.0.2564.116 Safari/537.36
PATH: /bin:/usr/bin
PHP_AUTH_PW: bigbadaboom
PHP_AUTH_USER: Longshot
QUERY_STRING: extended
REDIRECT_STATUS: 200
REMOTE_ADDR: 82.32.68.192
REMOTE_PORT: 57297
REMOTE_USER: Longshot
REQUEST_METHOD: GET
REQUEST_URI: /perch/core/settings/diagnostics/?extended
SCRIPT_FILENAME: /home/longshot/public_html/perch/core/settings/diagnostics/index.php
SCRIPT_NAME: /perch/core/settings/diagnostics/index.php
SERVER_ADDR: 162.13.44.160
SERVER_ADMIN: webmaster@longshot.photo
SERVER_NAME: longshot.photo
SERVER_PORT: 80
SERVER_PROTOCOL: HTTP/1.1
SERVER_SOFTWARE: Apache
UNIQUE_ID: VssE06INLKAAAHiAb-gAAAAH
PHP_SELF: /perch/core/settings/diagnostics/index.php
REQUEST_TIME_FLOAT: 1456145619.17
REQUEST_TIME: 1456145619
argc: 1