I too was getting reports of Yosemite issues. upgraded my macbook - and it appeared OK - but did see some oddness on one of our ssids (using PEAP)
debug logs for my client showed this:
Deauth from sta: 28:cf:e9:xx:xx:xx: AP 10.112.x.x-00:0b:86:xx:xx:xx-00-ap105-xxx Reason Tx fail reached maximum
noticed that for this particular ssid profile I had max-tx-fail set to 25
returning that value to 0 [default - unlimited fails allowed]
my macbook returned to its previously... more reliable state.
Let us know if your problem ssid profile also has a non-zero value and if changing that appears to help. I've only just made the change global in my environment so don't have any feedback - and the ssid impacted was for our students in the dorms.... feedback is not always a priority - and even less of a priority it seems when its positive :)
It was a setting I configured a while ago - with probe request threshold - to help mvoe sticky clients along - and prevent clients from making bad association decisions.... pre client-match
There's something about about allowing unlimited fails to get a device working.... I'm sure a source for much humor / life lessons - but lets get some feedback first