Downstream periodically goes down and has a huge amount of errors.

Long story short, about a year and a half ago I had my downstream going out (usually at night, when cold) and a tech came out and installed a signal booster in the basement. Fixed the problem until about a month ago when we started having significant drops in either upstream or downstream (one or the other. last time it was upstream, this time it's downstream.)

Every time I call support they want me to check the connections, reboot the modem, turn my PC off and on again, etc. I've done it all. I even let one of the phone people talk me into it being a bad modem (as my modem is DOCSIS 3.0). Changed the modem, zero change. Seriously, it was 100% fine earlier today, around 5 PM the downstream shot straight down to sub 1MBPS.  This same event happens 2-5 times per week.

Screenshot from modem showing uncorrectables

Anyone have any idea how to go about trying to fix this? Last time they sent a tech out to install the booster they tried to charge me $80. After a phone call they waved the fee, also they recently increased the price of my internet by 40% (which was somewhat reduced after a phone call, but still higher.)

Thanks for any insight you may have.