@The Chemist
I would suggest to replug in your Velop, power cycle everything and see what speeds you get using the Velops in built speed test first.
That'll tell you what you can potentially get up to using the default equipment and if the problem regarding the speed is your replacement router or the Community Fibre connection you have. As when I powered down my network entirely to swap plug locations on a surge protector after installation and just after installation, there was no training or sync period. It was your full speed and go once all powered and booted up.
Once you have the speed that can be obtained with the default equipment (the Velop), try the ethernet connection to it (Velop) with your laptop. This should tell us if the cable is bad or not (getting near everything of your speed on the ethernet means the cable should be fine, if not and only getting 100mbps, it's either your network port or the cable then that's the issue).
After this point, if all the above is fine, switch back to your replacement router and repeat the test with the ethernet cable to your laptop. If it's fluctuating, then the issue is on your replacement router.
If however, the Velop had fluctuating speeds as well, then there's a chance the issue is on your connection itself to Community Fibre. Contact Community Fibre about it.
Finally Your minimum speed should be 500mbps on a 1gb connection, so if it hovers in that region that'll unfortunately be your speed. Any less and contact Community Fibre about it.