Hey @lokapal, welcome to the forum + thanks for the info. 
Hmmmm… searching the internet for:
"error reading status line from remote server" Collabora
lead me to a handful of other older threads, like:
Looks like it might be some sort of Apache(?) + proxy/(firewall?) issue?
Here is another example of a user with same error + some proxy issues:
Hmmmm… well, I do have it running on Ubuntu 23.10 (Nextcloud/Docker) and Linux Mint 21.3 (+ standalone)… perhaps try a newer Ubuntu and let us know if it still works?
Edit: Whoops, I noticed this thread was 1 year old! I’m going to leave post up though, just in case it helps someone else in the future.