There's a typo in this commit:
https://github.com/opnsense/core/commit/b0aa1be38dcc2cd4f2ec41ee3302a182304b627d#diff-b22961b0c3e8876811f3f9c51bb8c833
+config_read_aray('ipsec', 'mobilekey');
Should be config_read_array
Indeed, apologies for this.
https://github.com/opnsense/core/commit/96119d9
Patched via:
# opnsense-patch 96119d9
And part of the upcoming 17.7.3.
Cheers,
Franco