Many years ago, when I first sought help from a computer techy, he didn't pay much attention to my long explanation of the problem.
He just smiled and rebooted my computer. "50% of the time, that's all it needs," he said.
I just remembered his wise words, so I switched off my router, read my newspaper for five minutes, then switched it on again.
After three days, problem solved.
Another lesson relearned.