I’m sorry to hear that this is still an issue on your end.
Unfortunately, I am not able to reproduce this on my end.
Would it be possible to have a few more details on where this is happening (post editor, site editor, user capabilities etc…) so that we can debug the situation?
Here is a quick summary, let me know if you need more information:
Page template for specific page
Code block containing multiple different elements at different times (e.g. first only PHP field was used, then PHP, CSS and JS were all used, then only CSS and JS were used, etc) - Issue occurred in all three cases.
Steps to repeat:
Add some content to the page template
Add a code block with some code in it
Save and view the page
Edit the page template contents without editing the code block OR edit the code block without editing the other page template contents
Save and view the page
Repeat steps 4-5 until you hit the issue - the code block contents are not rendered at all.
Note: When the issue occurs, editing the page template contents (without editing the code block) restores the page display to show correctly.