Description of problem:
IPSec/IKEv2 clients using EAP fail to connect to Strongswan after upgrade to 5.6.1

Version-Release number of selected component (if applicable):
strongswan-5.6.1

How reproducible:
Every time

Steps to Reproduce:
1. Configure Strongswan IKEv2 using EPEL 5.5.3 packages for EAP-RADIUS authentication. Verify connection works (in my case, MSCHAPv2 is used by the client and the RADIUS server uses ntlm_auth against AD).
2. Upgrade Strongswan to 5.6.1 from EPEL (via yum update)

Actual results:

Clients cannot log in any more. Charon log says: 
IKE verification of AUTH payload with EAP MSK failed

Expected results:

Clients should still be able to log in. 

Additional info:

The error occurs after EAP-RADIUS authentication succeeds (and EAP/SUCC is received by the client), when the client sends its last AUTH request expecting back a virtual IP address, DNS etc. 

End of the client log with 5.5.3:

Mar 16 18:17:46 assen-wifi.xentio.lan charon-nm[13914]: 14[ENC] parsed IKE_AUTH response 4 [ EAP/SUCC ]
Mar 16 18:17:46 assen-wifi.xentio.lan charon-nm[13914]: 14[IKE] EAP method EAP_MSCHAPV2 succeeded, MSK established
Mar 16 18:17:46 assen-wifi.xentio.lan charon-nm[13914]: 14[IKE] authentication of 'assen.totin' (myself) with EAP
Mar 16 18:17:46 assen-wifi.xentio.lan charon-nm[13914]: 14[ENC] generating IKE_AUTH request 5 [ AUTH ]
Mar 16 18:17:46 assen-wifi.xentio.lan charon-nm[13914]: 14[NET] sending packet: from 192.168.104.130[58216] to 213.144.1
39.34[4500] (112 bytes)
Mar 16 18:17:46 assen-wifi.xentio.lan charon-nm[13914]: 07[NET] received packet: from 213.144.139.34[4500] to 192.168.10
4.130[58216] (256 bytes)
Mar 16 18:17:46 assen-wifi.xentio.lan charon-nm[13914]: 07[ENC] parsed IKE_AUTH response 5 [ AUTH CPRP(ADDR DNS DNS) SA 
TSi TSr N(MOBIKE_SUP) N(NO_ADD_ADDR) ]

Same with 5.6.1

Mar 16 17:14:13 assen-wifi.xentio.lan charon-nm[13914]: 13[ENC] parsed IKE_AUTH response 4 [ EAP/SUCC ]
Mar 16 17:14:13 assen-wifi.xentio.lan charon-nm[13914]: 13[IKE] EAP method EAP_MSCHAPV2 succeeded, MSK established
Mar 16 17:14:13 assen-wifi.xentio.lan charon-nm[13914]: 13[IKE] authentication of 'assen.totin' (myself) with EAP
Mar 16 17:14:13 assen-wifi.xentio.lan charon-nm[13914]: 13[ENC] generating IKE_AUTH request 5 [ AUTH ]
Mar 16 17:14:13 assen-wifi.xentio.lan charon-nm[13914]: 13[NET] sending packet: from 192.168.104.130[58216] to 213.144.1
39.245[4500] (96 bytes)
Mar 16 17:14:13 assen-wifi.xentio.lan charon-nm[13914]: 04[NET] received packet: from 213.144.139.245[4500] to 192.168.1
04.130[58216] (80 bytes)
Mar 16 17:14:13 assen-wifi.xentio.lan charon-nm[13914]: 04[ENC] parsed IKE_AUTH response 5 [ N(AUTH_FAILED) ]

Client is Fedora 26, strongswan-5.6.0-1.fc26.x86_64.

The stock 5.5.3 RPMs work fine and manual downgrade resolvs the problem.