Steps to reproduce the issue

1. Create custom field group
Use name of your choice...

2. Create 3 custom fields
Use name and type of your choice...
Custom field 1: choose Options > Automatic Display: After title
Custom field 2: choose Options > Automatic Display: Before display content
Custom field 3: choose Options > Automatic Display: After display content
Then assign these fields to the previously created custom field group.

3. Create article
Use a title of your choice.
Use content text of your choice.
Insert a [Readon] button somewhere.
Fill in the three custom fields with content of your choice, but make sure you use three different contents for either of these fields.

4. Create menu item
Use menu item type «Category Blog».

5. Visit menu item in the frontend

Expected result

Before clicking [Readon] button
Custom field 1 should be placed underneath the article's title
Custom field 2 should be placed underneath custom field 1
Custom field 3 should NOT YET be visible

After clicking [Readon] button
Custom field 1 should be placed underneath the article's title
Custom field 2 should be placed underneath custom field 1
Custom field 3 should be placed after the article's content

Actual result

Before clicking the [Readon] button
Custom field 1 is not being displayed
Custom field 2 is placed underneath the article's title
Custom field 3 is placed underneath the [Readon] button

After clicking the [Readon] button
This works fine. All custom fields are placed correctly.

System information (as much as possible)

Joomla 5.3.0
PHP 8.4.6

Additional comments

I have the feeling that the options for «Automatic display» are not labelled correctly. The words seem to be twisted and therefore don't really make sense:

Automatic Display: Before display content
Automatic Display: After display content

From my point of view, a better labelling would be:
Automatic Display: Display before content
Automatic Display: Display after content