2GB service but getting sub 1GB speeds

I recently switched out the Xfinity Gateway which has 2 1GB ports for the Ubiquiti Unifi Cable Internet (UCI) modem, which has a single 2.5GB port. Initially, I was getting around 2GB speeds, but here lately, I've been getting sub 1GB speeds. I've even seen speeds as low as 300MBps down with ~320GBps up. Nothing else has changed with my network setup. I'm going from the UCI into my Unifi Cloud Gateway Ultra, which also has a 2.5GB port. The remaining 4 ports on it are 1GB but when I run the speedtest from the Unifi Network app,. I'm only getting sub 1GB speeds now whereas I initally got the 2GB speeds. I turned off my VPN settings, as I know that slows down speed, but it didn't help. Any suggestions on what else to do? The service was installed about 3 years ago and I had few issues up to now.