I’ve had this happen a couple of times and assumed it was just because the service(s) that didn’t show up were overloaded with brute force attempts etc, or maybe just the whole machine is running extremely slow and can’t service the network request. You have to remember these HTB machines run on pretty limited resources (only 1 CPU core and 2 GB of RAM is the maximum suggested when you submit a machine) and have potentially hundreds of people attacking them at once.
All I can suggest is either move your VPN to a different region so you get a different machine to connect to, or consider purchasing VIP which has way fewer people on each machine and generally just runs a lot smoother