By default trains wit roboport equipment in their grids only deploy robots in manual mode, this mod makes all trains (including modded) to deploy robots, even in automatic mode.
You can use the "Robots Inactive" wait condition (from vanilla) so that the train will wait for all robots before moving on. Beware though: if the cargo gets full the robots will just wait floating around outside until there is space to put their cargo and/or themselves.
Details: this mod sets
entity.allow_robot_dispatch_in_automatic_mode = true
for locomotives and cargo wagons.