Please open the site in Chrome, open DevTools (F12), reload the page, and check if you see any errors in the 'Console' when opening the editor. (see https://a3020.com/blog/basic-analysis-and-debugging-with-chrome-devt... if you want more information about DevTools)

Thanks for the tip.

Checked the js console with Dev Tools and throws up the attached error.
Any ideas?

My Settings:
# concrete5 Version
5.6.3.3

# concrete5 Packages
Automatic Email Obfuscator (1.2.3), Blueberry Image Slider (1.3), Fancy Image Links (1.3.8), Instant JavaScript (1.0.1), Login (1.1.1), PHP block by ND (1.0), Wall Gallery Suite (1.0).

# concrete5 Overrides
controllers/front, controllers/admin, controllers/index.php, js/cldr.js, js/validate.js, js/retro-compat.js.php, js/tiny_mce, js/cropper, js/tools.js, js/rtl.LICENSE, js/date.LICENSE, js/jquery, js/rtl.js, js/admin, js/fileuploader.LICENSE, js/vendor, js/fileuploader.js, js/admin-categories-tree.js, js/date.js, js/index.php, js/unicode_hack.LICENSE, js/admin.js, languages/fa_IR, languages/ru_RU, languages/cs_CZ, languages/ar, languages/es_PE, languages/sk_SK, languages/tr_TR, languages/el_GR, languages/fr_FR, languages/es_MX, languages/es_ES, languages/fi_FI, languages/nl_NL, languages/ro_RO, languages/it_IT, languages/da_DK, languages/vi_VN, languages/sl_SI, languages/zh_TW, languages/pt_PT, languages/nb_NO, languages/ja_JP, languages/de_DE, languages/sv_SE, languages/es_AR, themes/_libraries, themes/package-lock.json, themes/classic, themes/debug.tpl, themes/javascript.tpl, themes/core.js, themes/index.php, themes/KCL, tools/profiling, tools/parser_sql, tools/htmlpurifier, tools/index.php

# concrete5 Cache Settings
Block Cache - On
Overrides Cache - On
Full Page Caching - Off

# Server Software
Apache

# Server API
fpm-fcgi

# PHP Version
5.6.37

# PHP Extensions
bcmath, bz2, calendar, cgi-fcgi, Core, ctype, curl, date, dba, dom, enchant, ereg, exif, fileinfo, filter, ftp, gd, gettext, gmp, hash, iconv, imagick, imap, intl, ionCube Loader, json, ldap, libxml, mbstring, mcrypt, mysql, mysqli, mysqlnd, odbc, openssl, pcre, PDO, pdo_mysql, PDO_ODBC, pdo_pgsql, pdo_sqlite, pgsql, Phar, posix, pspell, redis, Reflection, session, SimpleXML, soap, sockets, SPL, sqlite3, standard, sysvmsg, sysvsem, sysvshm, tidy, tokenizer, xml, xmlreader, xmlrpc, xmlwriter, xsl, Zend OPcache, zip, zlib.

# PHP Settings
max_execution_time - 30
log_errors_max_len - 1024
max_file_uploads - 20
max_input_nesting_level - 64
max_input_time - 60
max_input_vars - 1000
memory_limit - 128M
post_max_size - 32M
sql.safe_mode - Off
upload_max_filesize - 32M
ldap.max_links - Unlimited
mysql.max_links - Unlimited
mysql.max_persistent - Unlimited
mysqli.max_links - Unlimited
mysqli.max_persistent - Unlimited
odbc.max_links - Unlimited
odbc.max_persistent - Unlimited
pcre.backtrack_limit - 1000000
pcre.recursion_limit - 100000
pgsql.max_links - Unlimited
pgsql.max_persistent - Unlimited
session.cache_limiter - nocache
session.gc_maxlifetime - 7200
soap.wsdl_cache_limit - 5
opcache.max_accelerated_files - 2000
opcache.max_file_size - 0
opcache.max_wasted_percentage - 5

It looks like it has trouble loading tinyMCE. From the list of overrides you provided, I noticed that 'js/tiny_mce' is also overridden. Maybe that's the cause of your problem?