@Kooven 

Before focusing on Deco mesh, you'll need to check quality of your cable Internet. Connect PC directly to Arris SB6190 by Ethernet cable and run your tests in that configuration for at least 24 hours. 

If there is still latency spikes and packet loss, that is either low cable signal quality or cable modem problems.

Technician was supposed to check for signal quality, but it is a good idea to double check by yourself. You should be able to check cable signal quality in status web pages of cable modem. I found helpful article for you, but I can't just copy external link, this form does not allow me to.

Instead, here is an image of the link to the article:

I googled your cable modem Arris SB6190 and one of the first reviews I saw states it overheats, up to the point of plastic discoloration and melting. This is bad, really bad. I think technician that visited your house might have known about that.

Make sure there is very good air flow around Arris SB6190. If cable signal quality is good, but packet loss and latency is bad, do consider replacing cable modem with different brand. It must be one your ISP supports. 

Now that you have Deco WiFi mesh, you could look for cable modem that does not have WiFi. That is probably an older model, but in this situation older may be better. If your ISP offers such cable modem (wired, but no wireless Internet), try it.

As for Deco mesh, it makes little sense to spend time on troubleshooting it, until you make sure your cable Internet is solid. The only thing I would suggest for Deco is to run it in Access Point mode, if you haven't done it yet. See How to set up Deco to work in Access Point mode?

In Access Point mode, Deco runs with lower CPU and memory utilization, which improves Deco mesh performance.

  @Alexandre. 

Thanks! I saw that review earlier last night as well, so I just switched out the ARRIS for a SB8200. So far things have been pretty stable, if things worsen again I'll run a test as per your suggestion and update this forum.