Upload Speeds Dropping to Near Zero Randomly

Starting about a week ago, my upload speeds will drop to very nearly zero (in the kb/s range) without fully reaching zero for usually half a minute or so. Meanwhile my download speed is remaining exactly what it should be at around 900 Mb/s. This seems to occur randomly throughout the day and sometimes doesn't even happen once in a day. I've have already conducted many of the standard troubleshooting steps. To name a few, restarting the modem/router doesn't seem to help, I've replaced the splitters leading to the modem, and I have checked on multiple devices and verified that it happens on all devices simultaneously. For additional information, I ran all my tests without a VPN and minimal traffic on the network, we have the rented xFi gateway, and I monitored my internet speeds, ping, and jitter using StarTrinity CST. From this I saw Tx packet loss of around 50-70% and jitter of upwards of 100ms during one of the observed downtimes. Once my connection returned to normal the Tx packet loss dropped to basically zero and the jitter returned to about 50ms. Any help fixing this or at least identifying the problem would be greatly appreciated.