I ran into this problem too after moving HA to new hardware (via backup/restore), while emonpi did not change. For some reason emoncms connection kep dieing and complaining about those max retries error. Reboots here and there brought it back for a little while and then ded again. But going to http://emonpi.local and logging in - the feeds and reporting was running no problem.
For me /emoncms was not an option because there’s nothing in that folder.
I’m not sure what network bs is/was the reason, because i did not change anything on router/emonpi side, but what helped was going from http://emonpi.local to http://ipaddress
Not the best solution but meh whatever, my emonpi ip is static lease in the router anyway.
Maybe helps someone else.