GS752TPv2 SFP Port Issues

Hello,

I recently attempted to switch from CAT6 uplinks for 2 of these switches to SFP uplinks after procuring a new router/firewall that has two SFP ports. Our firewall is a Sophos XGS 136 with 1gbps SFP ports. We purchased some 10Gtek branded DAC cables, model CAB-1GSFP-P1M, 1GBase-CU DAC 1-m, 30AWG, Passive, for CSC.

Upon switching over to these DAC's and removing the CAT6 uplinks, and rebooting all devices, we are unable to reliably pass data over the uplinks. Performing a ping test to the gateway and to google.com on a device on the switch results in multiple failed pings, as if the link goes up and down, and speed tests show a full 960mbps upload speed, but less than 1mbps download (should be closer to 1gbps both ways). On one of the switches, the link light eventually drops completely.

I have checked the config's on both the Sophos firewalls and switches and tried multiple ports on the switches as there are 4x SFP ports on each of them. I tried to change the configuration for the SFP ports on the Insight portal to 1000mbps and full duplex. I performed the same on the Sophos, setting them to 1000mbps full duplex and turning off auto-negotiation. With them both set manually, I have the same symptoms. I also tried setting it manually on just the switch, and also on just the Sophos, to no avail.

The switches are on the Insight portal and updated to the latest firmware, 6.0.10.14. The Sophos router/firewall is also on the latest firmware.

Could it just be bad DAC cables? Did I procure the incorrect cables? Does anybody have any suggestions on an alternative cable to use that is known to work with these switches?

Thank you!