Losing Internet in the evening than its back on in the morning.

For the past 2 weeks I've lost my internet between 9pm-12am.  I have called tech support when this happens and they can't see a problem on their end.  They sent a tech out and the tech had seen that over the course of the night the modem had reset itself over 100 times.  I was provided with a new modem but later about the same time a little past 9pm i lose internet.  I called tech support and they couldn't find anything wrong on their end.  I ran several speed tests and my speed was showing 10-20 mbs and almost no upload speed.  My normal speed is 350mbs and 20-25mbs upload.  I've reset the modem , updated my pc to the newest bios and chipset. Tech support says that because of Covid that they can no longer send any tech support to my home and that they will try to fix it on their end but if they can't see a problem then how can they fix it?  This is so dis heartening because my job is on the line.  If anyone has any help I would be most grateful.