I also have this problem, and then it will completely lose the connection requiring a scan to refind the router. After about 2 - 3 days a scan will no longer find the router and only a factory reset will recover the situation. I have raised the matter with Sony's technical support but they have seemed fit not to respond.
Over the years I have probably bought about 8 Sony televisions and this is undoubtedly the worst model. The support is non-existent!!!
