Hi,  @mrclark 
Thank you for posting on our business forum.
 

Please kindly find the troubleshooting recommendations below for your reference:

1.We have noted that the firmware version of your ER707-M2 is not the latest official release. Please upgrade it to the newest stable firmware, and check whether the issue still persists after the update.
2.We suggest performing a step-by-step check at the physical layer to locate the problematic device. You may first connect your PC directly to the ER707-M2, run a continuous ping test and check for abnormal latency or packet loss. Then you can repeat the same test when connecting through the TL-SG3452 and further downstream devices one by one, to pinpoint which device the issue originates from for subsequent troubleshooting. For your reference: if the problem still occurs when your PC is connected directly to the ER707-M2, the issue is very likely related to the gateway itself; if no abnormality is found in the direct connection test, you can continue to narrow down the problem among your downstream devices.
3.Once you have narrowed down the scope of the issue, you may use Wireshark for packet capture analysis. We recommend running a long-duration capture to check if there is any abnormal traffic exactly when the latency blips occur.

We would greatly appreciate it if you could share your relevant test results with us for further analysis.