There is a clear distinction between the two cases. First case: user record is found in users file:
rad_recv: Access-Request packet from host 192.168.2.1 port 2048, id=1, length=215 [skipped] +- entering group authorize {...} [skipped] [files] users: Matched entry 1510019760806391@wlan.mnc001.mcc510.3gppnetwork.org at line 1 [skipped] +- entering group authenticate {...} [skipped] Sending Access-Challenge of id 1 to 192.168.2.1 port 2048
Second case: user record is not found in users file:
rad_recv: Access-Request packet from host 192.168.2.1 port 2048, id=2, length=215 [skipped] +- entering group authorize {...} [skipped] ++[files] returns noop [skipped] +- entering group authenticate {...} [skipped] Failed to authenticate the user. [skipped] +- entering group REJECT {...} [skipped] Sending Access-Reject of id 2 to 192.168.2.1 port 2048
It seems your users file is broken in some way. You need to fix it.