Intermittent 502 error/ Article Editing Tools not operable

[ilox]

My Client is getting a 502 error every now and then. We have checked the settings for the Cloudflare servers and it all seems to be as required. He is also unable to get the Editing tools working such as Phoca Download / Image / Article Insert etc. I see them just fine, he can only see a link that does nothing once clicked.
We have tried changing settings within Firefox. Also accessing the site through Chrome and IE/Edge. No change for him. We have re-installed all the Phoca tools in case something had gone astray. I could see no change from my browser. He still could not make any Phoca tools (PhocaDownnload and Phoca Gallery) work.
He has checked that his Flash and JAVA are operating correctly and up to date.

Here is the output from FPA:

intermittent 502 error showing up

[26-Dec-2017 10:26:53 UTC] PHP Warning: session_start(): Cannot send session cache limiter - headers already sent (output started at /home/penscout/public_html/libraries/joomla/session/session.php:537) in /home/penscout/public_html/libraries/joomla/session/session.php on line 537

Checked DNS Records and all seems to be correct

Joomla! Instance :: Joomla! 2.5.28-Stable (Ember) 10-December-2014
Joomla! Platform :: Joomla Platform 11.4.0-Stable (Brian Kernighan) 03-Jan-2012
Joomla! Configured :: Yes | Read-Only (444) | Owner: --protected-- . (uid: 1/gid: 1) | Group: --protected-- (gid: 1) | Valid For: 2.5
Configuration Options :: Offline: 0 | SEF: 1 | SEF Suffix: 1 | SEF ReWrite: 1 | .htaccess/web.config: Yes | GZip: 1 | Cache: 0 | CacheTime: 15 | CacheHandler: file | CachePlatformPrefix: N/A | FTP Layer: 0 | Proxy: N/A | LiveSite: http://www.penarthanddistrictscouts.org.uk | Session lifetime: 15 | Session handler: database | Shared sessions: N/A | SSL: 0 | FrontEdit: N/A | Error Reporting: simple | Site Debug: 0 | Language Debug: 0 | Default Access: 1 | Unicode Slugs: 1 | dbConnection Type: mysql | Database Credentials Present: Yes

Host Configuration :: OS: Linux | OS Version: 3.10.0-327.4.4.el7.centos.plus.x86_64 | Technology: x86_64 | Web Server: Apache/2.4.27 (Unix) OpenSSL/1.0.1e-fips mod_bwlimited/1.4 | Encoding: gzip | Doc Root: --protected-- | System TMP Writable: Yes | Free Disk Space : 54.66 GiB |

PHP Configuration :: Version: 5.6.31 | PHP API: cgi-fcgi | Session Path Writable: Yes | Display Errors: 1 | Error Reporting: 24567 | Log Errors To: error_log | Last Known Error: 26th December 2017 10:26:53. | Register Globals: | Magic Quotes: | Safe Mode: | Open Base: | Uploads: 1 | Max. Upload Size: 20M | Max. POST Size: 8M | Max. Input Time: 60 | Max. Execution Time: 30 | Memory Limit: 32M

MySQL Configuration :: Version: 5.5.58-cll (Client:5.5.58) | Host: --protected-- (--protected--) | Collation: latin1_swedish_ci (Character Set: latin1) | Database Size: 13.75 MiB | #of Tables: 89

PHP Extensions :: Core (5.6.31) | date (5.6.31) | ereg () | libxml () | openssl () | pcre () | sqlite3 (0.7-dev) | zlib (2.0) | bcmath () | calendar () | ctype () | curl () | dom (20031129) | filter (0.11.0) | ftp () | gd () | hash (1.0) | iconv () | SPL (0.2) | json (1.2.1) | mbstring () | mcrypt () | session () | mysql (1.0) | standard (5.6.31) | Phar (2.0.2) | posix () | Reflection ($Id: 5f15287237d5f78d75b19c26915aa7bd83dee8b8 $) | mysqlnd (mysqlnd 5.0.11-dev - 20120503 - $Id: 76b08b24596e12d4553bd41fc93cccd5bac2fe7a $) | SimpleXML (0.1) | sockets () | imap () | tokenizer (0.1) | xml () | xmlreader (0.1) | xmlwriter (0.1) | zip (1.12.5) | cgi-fcgi () | PDO (1.0.4dev) | pdo_sqlite (1.0.1) | pdo_mysql (1.0.2) | Zend Engine (2.6.0) |
Potential Missing Extensions :: mysqli | suhosin |

Switch User Environment (Experimental) :: PHP CGI: Yes | Server SU: Yes | PHP SU: Yes | Custom SU (LiteSpeed/Cloud/Grid): Yes
Potential Ownership Issues: No

Core Folders :: images/ (755) | components/ (755) | modules/ (755) | plugins/ (755) | language/ (755) | templates/ (755) | cache/ (755) | logs/ (755) | tmp/ (755) | administrator/components/ (755) | administrator/modules/ (755) | administrator/language/ (755) | administrator/templates/ (755) | administrator/logs/ (---) |

Elevated Permissions (First 10) ::

Database statistics :: Uptime: 2343634 | Threads: 1 | Questions: 3411293 | Slow queries: 0 | Opens: 78351 | Flush tables: 1 | Open tables: 400 | Queries per second avg: 1.455 |

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[ilox]

PS: Yes, we know that it is an outdated platform. We had a full 3.5xxx site working but it was severely hacked through the Server so this is what we had to fall back to.
Yes, we had backups but they had been compromised.

[Per Yngve Berg]

Upload Size: 20M | Max. POST Size: 8M

A File upload larger than 8M will not fit in the Post. You have to fix this before you upgrade to J3.8.3

[ilox]

Umm, yes, OK, thanks for pointing that out. None of the files he would upload get even close to that limit.
So how does that relate to the error and the problems with the display and operation of the Article Edit tools that we are experiencing?