Radius authentication stopped working

I have a strange issue. It seems I broke the Wifi radius somehow (not really sure how or when, to be honest). I suspect I messed up the actual radius settings (we're using a Windows Network Policy Server as our radius server) but I failed to notice the issue when the change was made since existing clients could still connect.

Essentially it seems that devices that already have the Wifi connection saved can connect normally and without issues. However, a new computer cannot connect (Windows) and get's a rather generic "Unable to connect to this network" error.

Looking at the Wireless logs inside the UTM here's what I get:

2021:12:17-15:12:06 A4004D30532214D hostapd: wlan9: STA d4:1b:81:d7:4c:41 IEEE 802.11: authenticated
2021:12:17-15:12:06 A4004D30532214D hostapd: wlan9: STA d4:1b:81:d7:4c:41 IEEE 802.11: associated (aid 2)
2021:12:17-15:12:06 A4004D30532214D awelogger[24492]: id="4103" severity="info" sys="System" sub="WiFi" name="STA authentication" ssid="ARPCORPWLAN" ssid_id="WLAN3.1" bssid="00:1a:8c:c8:e8:46" sta="d4:1b:81:d7:4c:41" status_code="0"
2021:12:17-15:12:06 A4004D30532214D awelogger[24492]: id="4104" severity="info" sys="System" sub="WiFi" name="STA association" ssid="ARPCORPWLAN" ssid_id="WLAN3.1" bssid="00:1a:8c:c8:e8:46" sta="d4:1b:81:d7:4c:41" status_code="0"
2021:12:17-15:12:06 A4004D30532214D hostapd: wlan9: STA d4:1b:81:d7:4c:41 IEEE 802.1X: STA identity 'host/NTB-DELL-001.arp.local'
2021:12:17-15:12:06 A4004D30532214D hostapd: wlan9: STA d4:1b:81:d7:4c:41 IEEE 802.1X: authentication failed - EAP type: 25 (unknown)

Any idea what's going on?

EDIT: I may have been wrong about the initial assumptions that existing clients can connect. It seems that I am able to connect from my phone... but not from Windows. So this seems to be a Windows issue, somehow. Normally I'd get a prompt on Windows if I want to trust the certificate - this time I'm not getting one (on my phone I can chose to ignore the certificate immediately).