I am having trouble with my 2degrees internet connection.

My network topography

ONT - Huawei HG8240H

Router - Ubiquiti EdgerouterX (powered from POE injector) or Skinny Smart Modem (Arcadyan VRV9517)

Switch - Ubiquiti USW-Lite-8-POE

AP - Ubiquiti U6-Pro (powdered from POE switch)

Bridge Ubiquiti NBE-M5-16 (powered from POE injector)

Remote switch - Ubiquiti USW-FLEX-MINI (powdered from POE switch)

I have intermittent access to web traffic that cycles on a 30 second period. This has been happening since about mid-September. Prior to this the connection was working great for 10 months.

I observe this in the following situations

 

1. Internet browsing through a web browser on desktop; Firefox.
2. Internet browsing through a web browser on mobile devices; Firefox, Samsung Browser.
3. Browsing on apps like Reddit, Facebook, Trademe, Aliexpress.
4. Can't play online games without dropouts.

Error message on web browser:
Unable to connect

An error occurred during a connection to www.google.com.

I have called 2degrees support multiple times and done the following:

 

1. Get my ONT serial number (I wasn't home at the time, so had to call back when I was home again, but no one ever asked for it again, so I really wonder the value of this request or if it was just busy-work to get me off the phone).
2. They run "diagnostics" from their side and see no errors.
3. Replace the ethernet cables between my ONT and Router, and Router and Switch.
4. Network equipment is in a cupboard, so maybe overheating. Equipment is warm, but not hot Left the cupboard open all day and noticed no differences.
5. Lodged a fault. I got an email with "Hi there, Just a quick note to let you know that we’ve fixed your fault". I called them up to get some more details and found that the ticket was closed with no fault found. That email is quite misleading.
6. Pay $20 to get a 2degrees modem because they cannot help me further if I don't do this.

Things I have tried/observed

 

1. I was able to ping my router and ping an external server using ping -t for half an hour with no responses over 20 ms and no errors from a desktop on my network. During this time browsing was intermittent.
2. Replaced my router. I was using the Skinny Smart Modem, but started to get these issues and switched to the Ubiquiti EdgerouterX to see if that would help.
3. Attached a desktop PC direct to the router (bypass the switches).
4. I can connect with my work laptop (uses secure remote access) and have uninterrupted connectivity.
5. Updated firmware on all Ubiquiti equipment.

I am at a loss as to what to do next. My contract with 2degrees ends this month, would another provider make any difference? Any other suggestions or ways to diagnose?

(EDIT: trying to fix formatting because I have tried to post this a few times due to connectivity errors so copied this post to a document so I didn't lose it)