Hi, mak..
By the subject type of your thread, i think it is time for you to repair the windows. I do not say , reinstalling , but repairing windows.
I have tried your suggestion of ipconfig/flsuhdns. I set it in my pc using task scheduler. I could just see it is working nicely.
Your task schedule is having bug, which cannot be corrected in any other manner than repair windows.
I have tried so much methods on corrupted task scheduler and none worked. I adopted new install. If the task schedule is at fault, then the system has strange entries in your registry.
There are programs in microsoft that repair registry, but i doubt, they do not move any injurious entries in the registry , leaving the problem not solved. but if you repair, those entries are killed and your computer is clean. Chkdsk sfc would not do much in such circumstances, as far as i know.