I contacted their support and test it in all my domains even though it is work in nginx side. Cloudflare also work. Only when only add bunny cdn as reverse proxy it didn't work. They said i am the single user on the plannet that has this weird problem. I really want to make sure I am the one who face this problem. To be fair, unless someone use bunnycdn as reverse proxy I cannot confirm their claim. I believe the the issue is wordops doesn't have support zstandard so when the post request is zstandard it fails.
Have you whitelisted the Bunny IP's?
No.
Regarding this I dont believe it is required since it is only login logout not working so page loads perfectly.
Does really fail2ban log check helps. I really dont think so. But I have to check this last part. Not sure why fail2ban blocks because i tested cloudflare, cloudfront both are working. If i dont have any 500 or 400 error where u checked. Unless someone checks bunny as reverse proxy I cannot deny or agree their claims.
How can default server configuration which i dont add anything blocks bunny because in previous times, i was given har files and they said zstandard post request sending but since nginx is not getting as gzip, brotli causing the error. I request in future update, wordops comes with zstandard compresssion support.