I managed to reproduce the behavior on a new, fresh minimal Joomla install on my own computer. The site and database can be found here:
https://drive.google.com/file/d/1-aCdKQRSIwZ-zX4YKCx0mh7xboKyD6w2/view?usp=sharing
it's a jpa archive created with the akeeba backup extension which I also use to deploy joomla sites. It can be unpacked on any webserver using the akeeba kickstarter:
https://www.akeeba.com/download/akeeba-kickstart/7-1-0/kickstart-core-7-1-0-zip.zip
akeeba is not needed to reproduce the bug - it was already reproducible before the akeeba plugin was installed. the only installed extensions were
- template Purity iii
- T3 plugin
- JCE editor
System setup:
On localhost:
Apache/2.4.41 (Ubuntu)
PHP 7.4.3
MySQL 8.0.27
On the webserver:
Apache(Debian)
PHP 7.4.26
MySQL 8.0.27
I hope this is sufficient to reproduce and debug the issue.