Hi there! Since this is your first post, you should take a read of Please read: make it easier to help you. It’s easier to help if you can provide a reproducible example, instead of isolated lines.
After optimization, OP_t is 0 while all parameters and variables are non null and non negative.
Did you take a look at termination_status(obj) to see if Gurobi found a feasible solution? Apart from that, it’s hard to tell what’s going on without a reproducible example. Gurobi shouldn’t find a solution with the equality violated.