I had the same problem with random internet drops and massive spikes. What fixed it for me was going into antenna settings in "system -> antenna" and changed the 'Select Mode:' from 'Auto' to 'Fixed' and apply. You can change the 'Antenna Combine Index', it's the combination of antennas which can be used on the device. The arrows in red shows the antenna combination for the selected 'Antenna Combine Index', more details can be read in the user help manual (as shown below). The 'TX Antenna' is the antenna currently used, respective to the 'Antenna Combine Index'.
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I notice the random drops and spikes happen when the 'Select Mode:' is in 'Auto' and the router auto selects an antenna combination which is not optimal and packets starts dropping. An incorrect 'Antenna Combine Index' will use the incorrect antenna and leave you with no/slow internet.
Hope this will help you, as this helped me and my connection is now rock solid.
Edit: The manual can be found when you log into the CPE and click on the 'help' button on the top right.