I have the following multiobjective optimization problem

I am using both Gurobi and Mosek to solve this. The program runs for ever.

The objectives are non-conflicting.

\textbf{The Optimization problem:}

\begin{array}{*{35}{l}} \underset{a^{(l)}_{c,u},f^{(l)}_{c,u},z_{l,t},l\in\mathcal{L}}{\max}\hspace{6mm}t^{(1)}_{\rm U},\underset{a^{(l)}_{c,u},f^{(l)}_{c,u},z_{l,t},l\in\mathcal{L}}{\max}\hspace{6mm}t^{(2)}_{\rm U},\cdots,\underset{a^{(l)}_{c,u},f^{(l)}_{c,u},z_{l,t},l\in\mathcal{L}}{\max}\hspace{6mm}t^{(N_{\rm L})}_{\rm U},\underset{a^{(l)}_{c,u},f^{(l)}_{c,u},z_{l,t},l\in\mathcal{L}}{\max}\hspace{6mm}t_{\rm L}\\ \end{array}

Since there is no preference (all the objectives have the same priority), I tried with the following objective.

\underset{a^{(l)}_{c,u},f^{(l)}_{c,u},z_{l,t},l\in\mathcal{L}}{\max}\hspace{6mm}\sum_{l=1}^{N_L}t^{(l)}_{\rm U}+t_{\rm L}

I am not sure if I am doing it right.

So, how can I resolve this issue. Is the single objective that I am using correct?