Internet speed dropped after an otherwise seamless upgrade and restore

Hello everyone

I upgraded my Asus RT-AC85p to 23.05 and in every respect it went perfectly. Both the upgrade and restoring from backup worked beautifully and all my settings are the same. The only problem is that my speed has dropped from 500mbps to 320mbps and I can't fathom why.

I remember when I first installed 22.03.5 I had to enable hardware offloading to get the full 500mbps speed and that setting was preserved in 23.05, I have even disabled and enabled it again after reboots and still only attain ~320mbps. I'm going crazy here, does anyone have any insight or recommendations please? Thanks very much.

Usually the first test in these cases is to bypass the router and connect the measure computer directly to the ISP connection and verify the speed reduction so we know the fault is in the router.

Next step is trying firmware default settings, if full speed is then achieved we end up in the fact that some of your configs are non-working between mayor version upgrades.

When upgrading from one major version to another, e.g 22 to 23, it is not advised to keep the settings nor restore the backup of another version.
Start clean and use the backup file as reference to configure the router.