404 Errors after I click “Save settings and force new .htaccess rules”

My production website’s images crushed a few days ago, and I asked hosting team (siteground) to check it. They couldn’t fix it and asked me to restore from backup. At that time I didn’t have any idea that it was caused because I was tring make the Webp Express plugin work.

Since the same issue occured again, I realised that the cause is Webp Express. But other than the crush problem, the more problematic thing is that I installed Webp Express to my staging folder, and it crushed my production.

How to re-create issue on my website:

Pre-information:

My Site: https://www.example.com
My Staging: https://www.staging1.example.com
Example image link: images.example.com/imagename.jpg (They are in a subfolder)

1- Activate the plugin in staging1.example.com
2- Click “Save settings and force new .htaccess rules” immediately.
3- All images starts to give 404. Image links also.