for me it looks like Apache is not handling/passing the requests through or PHP is not Processing it.
a few Questions to narrow it down:
- can you access your Cloud per domain name? (Browser)
- can you access it with IP? (also in Browser ,you may need to add the IP to the Trusted Domains)
- what is happening when you use
curl https://cloud.YOURDOMAIN.com/remote.php/files/YOURUSER(Commandline, change the Points in Capital letters according to your setup) - Is it happening mutually? so e.g. Server 1 can reach server 2 but not the other way around?