We have a similar (probably the same) problem - plagueing us for a while now. We use IKEv2 EAP-Radius with aes256-gcm on an SG-8860 on a 1gb fiber uplink.
When one of our users (he is on 100mbit fiber) tries e.g. speedtest.net while on the VPN, the pfsense box reliably crashes after a few seconds of upload (download works fine). When I try this at home on a 100mbit/40mbit DSL link, I can create all the traffic I'd like and can't get the box to crash.
I now switched algorithms to AES-256 with SHA512 (still with AES-NI, I didn't disable that) and it seems the crashes have either gone away or we weren't yet able to reproduce them today.
Kind regards,
Lukas