Has Yosemite been Deprecated by Blizzard, yet??? I’m NOT sure where Yosemite stands right now, if it is still “Playable” by Blizzard Specs. It may be close to End Of Life here.
Wait for a Blue Post to chime in, of course. I know that 10.9 was EOL some time ago, so be on the lookout for Yosemite to EOL soon.
Sorry for the bad news.
TimeLord04
[EDIT:]
IF possible, try to Update to AT LEAST El Capitan. Then try Re-Launching your games. IF successful under El Capitan, then you’ll have your answer, and prove my suspicions right that Yosemite has hit EOL here.
Good Luck.
TimeLord04