Minimization Terminated in Bootstrapping

Dear NM users: I have a data set where the absorption phase is highly variable. A complicated absorption model (the TRANSIT model) significantly improve the model fit (OFV drops over 250) compared to a 1st-order absorption model with lag time. The complicated final model converged and the covariance step was successful. The condition number is low (less than 10), although there were many runs with rounding errors during model development. However, in the bootstrap analysis,about 600 out of 1000 iterations had minimization terminated which leads to a successful rate of only 40%. My question is: is there any consensus regarding the acceptable successful rate for bootstrap analysis? I understand 40% is very low. Should I reject this model then? Any suggestions will be greatly appreciated. Thanks, Siwei