We have as well, I have 6 NG firewalls, 2X NG F300, 2x NG F200, 2x NG F100's across my org, and we also had the cudatel.
We recently replaced the cudatel with 3cx which went well, but now my NG Firewalls are all running extremely slow and NG Admin just hangs.
Please don't see this as simply making an excuse; but the NG F100/F200/F300 models are based on VIA CPUs which completely prioritise low power consumption over performance. I don't know what environment you're using them in, but my opinion is that they simply don't scale at all well. We stopped selling them all in 2015 for this very reason, they're very much end of life at this point.
If you've had active subscriptions on them for several years and are otherwise happy with the feature set that the firewall offers, it would definitely be worth your while speaking to Sales/Renewals to see if there's any kind of deal they can cut you to upgrade your hardware - the modern equivalent of those models (which I would see as the F12/F18 models, maybe up to an F80 for the F300 replacements depending on whether they can be rack mounted) are based around better performing CPUs and storage, so they really are worlds apart from the old F100/F200/F300 models even though I believe they're roughly the same price point. I've run other firewall distributions such as pfSense on similar VIA hardware, and to be frank, everything performs poorly on them. They're a 2005 CPU design heavily biased towards low power consumption, they won't work for everyone's use case.
I've licensed all my devices, but many of them still say unlicensed, I don't know what the hell is going on, but now I am shopping for firewalls too.
Did you open a Support case about this? I know we have had some issues in the past with older boxes failing to license themselves automatically, however if this fails then you should be able to install the license files manually as a one-off operation.
UBNT's 16 core box looks really nice, and it's comparable in price to the NG when I bought it. I'll be happy to get away from NG Admin.
I generally like Ubiquiti products and use Unifi access points both personally and in our branch office - but I haven't heard great things about their other product ranges in professional environments. Read into that what you will, working for a firewall vendor there is likely to be some bias in my opinion...