Unable to Update Craft CMS & Plugins [duplicate]

Question

When trying to update CraftCMS I'm getting the following errors:

Error: An error occurred

Output: Loading composer repositories with package information
Updating dependencies
Your requirements could not be resolved to an installable set of packages.

Problem 1
- Installation request for craftcms/cms 3.0.21 -> satisfiable by craftcms/cms[3.0.21].
- craftcms/cms 3.0.21 requires enshrined/svg-sanitize ~0.9.0 -> satisfiable by enshrined/svg-sanitize[0.9.0] but these conflict with your requirements or minimum-stability.
Problem 2
- craftcms/ckeditor 1.0.0-beta.2 requires craftcms/cms ^3.0.0-RC1 -> satisfiable by craftcms/cms[3.0.21].
- craftcms/ckeditor 1.0.0-beta.2 requires craftcms/cms ^3.0.0-RC1 -> satisfiable by craftcms/cms[3.0.21].
- craftcms/cms 3.0.21 requires enshrined/svg-sanitize ~0.9.0 -> satisfiable by enshrined/svg-sanitize[0.9.0] but these conflict with your requirements or minimum-stability.
- Installation request for craftcms/ckeditor 1.0.0-beta.2 -> satisfiable by craftcms/ckeditor[1.0.0-beta.2].

Running update with --no-dev does not mean require-dev is ignored, it just means the packages will not be installed. If dev requirements are blocking the update you have to resolve those problems.

The problem is, the following is all OK:

• composer update comes back with "Nothing to Install"

Answer 1

The original composer file that caused the error above looked like this:

{  "name": "craftcms/craft",
"description": "Craft CMS",
"keywords": [
"craft",
"cms",
"craftcms",
"project"
],
"license": "MIT",
"homepage": "https://craftcms.com/",
"type": "project",
"support": {
"email": "support@craftcms.com",
"issues": "https://github.com/craftcms/cms/issues",
"forum": "https://craftcms.stackexchange.com/",
"source": "https://github.com/craftcms/cms",
"docs": "https://craftcms.com/docs",
"rss": "https://craftcms.com/changelog.rss"
},
"require": {
"craftcms/cms": "3.0.13.1",
"vlucas/phpdotenv": "v2.4.0",
"craftcms/ckeditor": "1.0.0-beta.2",
"craftcms/redactor": "2.1.5",
"cebe/markdown": "1.1.2",
"composer/ca-bundle": "1.1.1",
"composer/composer": "1.6.3",
"composer/semver": "1.4.2",
"composer/spdx-licenses": "1.3.0",
"craftcms/oauth2-craftid": "1.0.0.1",
"craftcms/plugin-installer": "1.5.2",
"craftcms/server-check": "1.1.1",
"creocoder/yii2-nested-sets": "0.9.0",
"danielstjules/stringy": "3.1.0",
"doctrine/lexer": "v1.0.1",
"egulias/email-validator": "2.1.4",
"elvanto/litemoji": "1.3.1",
"enshrined/svg-sanitize": "0.8.2",
"ezyang/htmlpurifier": "v4.10.0",
"guzzlehttp/guzzle": "6.3.3",
"guzzlehttp/promises": "v1.3.1",
"guzzlehttp/psr7": "1.4.2",
"justinrainbow/json-schema": "5.2.7",
"league/flysystem": "1.0.44",
"league/oauth2-client": "2.2.1",
"mikehaertl/php-shellcommand": "1.2.5",
"paragonie/random_compat": "v2.0.12",
"pixelandtonic/imagine": "v0.7.1.3",
"psr/http-message": "1.0.1",
"psr/log": "1.0.2",
"seld/cli-prompt": "1.0.3",
"seld/jsonlint": "1.7.1",
"seld/phar-utils": "1.0.1",
"swiftmailer/swiftmailer": "v6.0.2",
"symfony/console": "v3.3.6",
"symfony/debug": "v3.3.6",
"symfony/filesystem": "v3.3.6",
"symfony/finder": "v3.3.6",
"symfony/polyfill-mbstring": "v1.8.0",
"symfony/process": "v3.3.6",
"twig/twig": "v2.4.8",
"yiisoft/yii2": "2.0.15.1",
"yiisoft/yii2-bootstrap": "2.0.8",
"yiisoft/yii2-composer": "2.0.6",
"yiisoft/yii2-debug": "2.0.13",
"yiisoft/yii2-queue": "2.0.2",
"yiisoft/yii2-swiftmailer": "2.1.1",
"zendframework/zend-escaper": "2.6.0",
"zendframework/zend-feed": "2.8.0",
"zendframework/zend-stdlib": "3.2.0",
"solspace/craft3-freeform": "2.2.1"
},
"autoload": {
"psr-4": {
  "modules\\": "modules/"
}
},
"config": {
"optimize-autoloader": true,
"platform": {
"php": "7.0"
}
},
"scripts": {
"post-root-package-install": [
"@php -r \"file_exists('.env') || copy('.env.example', '.env');\""
],
"post-create-project-cmd": [
"@composer dump-autoload -o",
"@php craft setup/welcome"
]
}
}

So I removed "enshrined/svg-sanitize": "0.8.2", from the list in the compser file, and ran the update. The next error was given for Twig. So I deleted ""twig/twig": "v2.4.8" from the file, and ran the update again. This time it was successful, and the composer file now looks like this:

{
"name": "craftcms/craft",
"description": "Craft CMS",
"keywords": [
"craft",
"cms",
"craftcms",
"project"
],
"license": "MIT",
"homepage": "https://craftcms.com/",
"type": "project",
"support": {
"email": "support@craftcms.com",
"issues": "https://github.com/craftcms/cms/issues",
"forum": "https://craftcms.stackexchange.com/",
"source": "https://github.com/craftcms/cms",
"docs": "https://craftcms.com/docs",
"rss": "https://craftcms.com/changelog.rss"
},
"require": {
"craftcms/cms": "3.0.20",
"vlucas/phpdotenv": "^2.4.0",
"craftcms/redactor": "2.1.5"
},
"autoload": {
"psr-4": {
"modules\\": "modules/"
}
},
"config": {
"optimize-autoloader": true,
"platform": {
"php": "7.0"
}
},
"scripts": {
"post-root-package-install": [
"@php -r \"file_exists('.env') || copy('.env.example', '.env');\""
],
"post-create-project-cmd": [
"@composer dump-autoload -o",
"@php craft setup/welcome"
]
}
}

So the update seems to remove a lot of the required references in the composer file. I tried doing this on a backup install first before doing the same on the live install.