Internet randomly dropping

For the past week or 2 my internet has stopped working for seemingly no reason at all at random multiple times. My isp is spectrum, and when the problem happens all my online lights are all normal on both the modem and router, but nothing will load on any device. I have tried hard resetting both devices, and spectrum sent a technician out, and he said my signal was too strong originally and put a splitter in to balance it, and insisted that if I have any problems it's an issue with my router, but I don't know what to believe. I've had an xr500 for over a year now and it's had some obvious bugs but this problem just started a week or so ago, so it's hard to believe it's a problem with my xr500.