MB air force closes all applications in standby mode

Hi, I am running Yosemite 10.10.5 on my MBA MID 2013 256GB SERIAL NO C02L42CXF5V8

very recently I am facing a strange behaviour of my MBA, every time I leave it in standby mode, not in sleep mode,

each and every opened applications are force closed automatically and I have to restart them. which is quite annoying.

Any help please. Thanks