I have had Verizon FiOS Gigabit for about 9 months now. Prior to that I had spectrum but left them because they limit the upload speed to 35mbps. However, MY router (Netgear RAX120 Wifi 6) would consistently provide between 500-700MBPS over Wifi 6 and between 300-500 on Wifi 5, both on 5G obviously.
Since switching to Verizon FiOS, my wifi speeds are always just in the 100s usually - between 120 and 150 on average, with Peaks of maybe 180-200 on rare occasions.
Initially, I had the Verizon Wifi 6 Router and Coax MoCA connected Wifi 6 Extender - Same speeds there so I thought may as well use my own equipment, but no luck. The Wifi settings weren't changed between the switch from Spectrum to FiOS.
Another thing is if the Router does a speed test from itself to Verizon, the Speed is 900+. But the Wifi Connected clients get kicked down to the 100s. I have taken the Router to someone who has spectrum and just connected their WAN cable to the router and from a cold boot, I was able to get a full 400mbps on Wifi 6 on their Spectrum plan, so obviously, the router is ok..
All Wifi settings are for Max Performance - changing channel widths make no difference - and the same no of devices are around, creating relatively the same level of interference. Even connecting Meraki MR55 Wifi 6 Access Points (retail over $1000) make no difference even though if I take the SAME CAT5 cable that went over to the Meraki and connect it directly to a computer, the Speed will be 800+ Mbps on Average, but doing a speed test yields just 130.
It's really incredible how this is happening. Hopefully, someone here has a solution?
My other thought is, if you have automatic speed test or QoS enabled on your router, sometimes they generate the maximum bandwidth value by using a built-in speed test. I would make sure those features are turned off before trying to test again.