Apple Remote Management & Screen Sharing fails on Yosemite

I have a MacBook Pro at home attached to the Internet.

I have a MacPro and an iMac in my office in town attached to the Internet.

I was able to access my various computers reasonably successfully using Remote Management under Mavericks.

Since Yosemite, the connections are variable in that occasionally machines appear on the network, and sometimes they don't. Sometimes they remain visible in the Finder sidebar, even though the machine is switched off (e.g., my MacPro in my office is listed as available on my MacBook Pro at home).

I thought I'd cracked it by switching back to Screen Sharing from Remote Management... but no, the randomness crept back in.

I have never had to fiddle with the settings, it just used to work. Now it seems I need knowledge of networks, VPNs, SMBs, and all such other technical things.

At the moment it's quicker to get a memory stick and walk from home to my office with the data than try and get this to work!

Anyway, if someone could tell me whether or not I'm wasting my time, i.e., it's a bug in Yosemite, that would be handy.

Many thanks.

James