Description

I had created a matrix field earlier in the week with several block types while in version 3.3.x and then updated to version 3.4.1 yesterday. Sometime after the update, I created a new block type, added a field, and saved it, then I got an error. From the logs:

2020-01-31 01:18:17 [-][1][op4ovmv6f9nluvrgh8poqhbdat [error][yii\base\ErrorException:1] yii\base\ErrorException: Unknown: Input variables exceeded 1000. To increase the limit change max_input_vars in php.ini. in /Users/me/Sites/MWC/vendor/yiisoft/yii2/base/ErrorException.php:43
Stack trace:
#0 /Users/me/Sites/MWC/vendor/craftcms/cms/bootstrap/web.php(51): ::unknown()
#1 /Users/me/Sites/MWC/web/index.php(20): ::unknown()
#2 {main}
2020-01-31 01:18:15 [-][1][op4ovmv6f9nluvrgh8poqhbdat][info][application] $_GET = [
    'p' => 'mwclogin/settings/fields/edit/37'
]

I had googled around searching for Input variables exceeded 1000. To increase the limit change max_input_vars in php.ini but a few SO responses said that increasing the limit was not the right thing to do, that it's a solution to the wrong problem.

Steps to reproduce

1. Create a matrix field in version 3.3.x
2. Update to 3.4.1
3. Add a new block type to existing matrix field
4. Add a text field
5. Save the field
6. See the error

Here's a gif:

Just to be clear what's going on in the gif, I'm scrolling down to create a new block type in my existing matrix field called "Test", I create a new plain text field called "Test", and I save the field and see the error.

Additional info

• Craft version: 3.4.1
• PHP version: 7.3.9
• Database driver & version: MySQL 5.6.21