Shares goes offline after 3 days, FrontView still working

After about 3days of uptime I cant acces my shares from either Windows or Linux (Ubuntu). Says that the network resource could not be found. I can still acess the shares from http://readyNasIP/shares and the frontview is still working. A reboot fixes this issue. But after about 2-4days the same thing happens again. Happened 3 times allready. I have the Pro 4 and I need great uptime. I cant keep rebooting when I cant acess the shares. What could be the problem? The logs are all OK (shows green light atleast).