With debugging turned on, I get:
Nonce Expired. Your NonceLifeTime may be too short at /opt/webwork/webwork2/lib/WeBWorK/Authen/LTIAdvanced.pm line 687.
$NonceLifeTime = 60 in the LTI_authen.conf seems insufficient. Experimentation gives 120 as the roundest and lowest value which does not generate the error.
Nonce Expired. Your NonceLifeTime may be too short at /opt/webwork/webwork2/lib/WeBWorK/Authen/LTIAdvanced.pm line 687.
$NonceLifeTime = 60 in the LTI_authen.conf seems insufficient. Experimentation gives 120 as the roundest and lowest value which does not generate the error.