Sudden Slow Upload Speeds

About 2 weeks ago my upload speeds dropped dramatically. I was averaging around 40 Mbps. Now it's typically around 1.0 Mbps. Download speeds have remained consistent around 800 Mbps like they've always been. The poor upload speeds have had a detrimental effect on web conferencing and not surprisingly, uploading files! 

The modem (Motorola MB8600) has been rebooted numerous times. Bypassing the router and connecting a device directly to the modem resulted in no improvements in the poor upload speeds. When running the xfinity network test/restart modem utility, sometimes the modem is unable to be located even though it's clearly back online.

The modem has 32 downstream bonded channels and 5 upstream bonded channels with all parameters within norms.

I've been traveling so it hasn't been an issue. Now that I'm back, it's a big issue! Any ideas?

Thanks

John