AlwaysOn VPN ikev2 slow and bandwidth varies a lot

RAS Server: Windows Server 2022 Core

NPS: Windows Server 2012 R2 (also a DC)

Router: Lancom 7100+ VPN

I basically followed this Guide and the User Tunnel works fine, it connects automatically and we can reach the internal network via rdp, ssh, smb and so on.

We have two issues:

1. The bandwidth fluctuates between 3,47 and 41,7 Mbit/s with a mean of 17,6 Mbit/s measured by iperf
2. SMB is slow - it could be the sporadic drop in throughput or the increased latency

The VPN is usable as in we can reach the device to administer it, but it's not good enough for our remote workers. Does anybody know if I can perfomance tune anything?

As a comparison my L2TP VPN (Certificate Authentication with the same NPS) has a pretty stable throughput of 63,5 Mbit/s.

If any additional information is needed just ask and I will provide it.