File sharing not working in High Sierra - help

Help. I have a brand new iMac running High Sierra. I have 3 other, older iMacs on my home network. One of these machines (let's call it #1) is running Mountain Lion. Two of these machines (#2 and #3) are running Sierra. The new Mac (#4) is running High Sierra.

On each machine, the other 3 machines are visible in Finder as "shared". Sharing among the older machines (#1, #2, #3) works fine, as it always has. Sharing with the new iMac (machine #4) is pretty broken.

With Machine #2 (Sierra) I can connect but I get a message "connected as com.apple.idms.prd.and then a very long numerical id. But sharing works. With Machine #3 (Sierra) and Machine #1 (Mountain Lion) any attempt to connect results in "connection failed.

Going the other way (from Machine #4 High Sierra) works connecting *to* any of the other machines.

Help.