" I tried sudo yunohost service status and “send” does not appear in the list, nor is it in the Services page from the webadmin."
send is installed and no service name “send”, well thats something only aleks can help with,
i do have send service on my server,
i noticed something strange in your log, to the best of my understanding its looks like port 8095 trying to be in use for send?!
i have send installed and i dont have any requirement for port 8095, its not even on the firewall list on my server,
because you did involved an external dynamic dns server there is a possibility namecheap dns servers drops some traffic,
i don’t know if aleks have a better idea but if you’re asking me, you should test your server with an reliable DNS provider,
if you want to do so for completely free, please just follow my reply on this thread:
or the other option is: just get a domain from yunohost at least you will own it for testing purposes and second domain will anyway give you an second option to reach your server,
the reason i still think you should try with another domain, it is not because “send” its because earlier you mentioned you have the same problem with other subdomain apps as well sometimes,
and don’t forget to close back your ports on your router after you done testing, such open range is very vulnerable