I found your HAProxy configuration in your "Draft installation guide." It seems you're using regular TCP streaming mode with the Snowflake instances vs transparent TCP streaming mode, which is a notable difference with the directly loadbalanced Tor Relay configuration. I also noticed you've configured the backend node timeout globally vs per node, which is just a nuance. You might test using a timeout value of 0s (to disable the timeout at the loadbalancer) and allow the Snowflake instances to preform state checking to ensure HAProxy isn't throttling your bridge. I've tested both and I'm still not sure which timeout configuration makes most sense for this style implementation. Currently, I'm running with the 0s (disabled) timeout.

Any reason why you chose HAProxy over Nginx?

I did notice that you're using the AssumeReachable 1 directive in your torrc files. Are you running into an issue where your Tor instances are failing the reachability test? Initially, I ran into a reachability issue and after digging through mountains of Tor debug logs discovered I needed to use transparent TCP streaming mode along with the Linux kernel and iptables changes to route the Tor traffic back from the Tor Relay Nodes to the loadbalancer. You shouldn't need to run your Tor instances with the AssumeReachable 1 directive. This might suggest something in your configuration isn't quite right.