Sounds weird! Just to make sure that you have really done everything, you have
1. created a track and a track back to where you've started. The tracks have names, they are both checked for errors and are both working. The terminus is not the same bus stop dice as the start of the tour back.
2. created trips and you have made sure that in them
a) you have marked the track segment next to the bus stop dice, so that it turns yellow
b) you have a profile linked to the track
3. made a timetable in which
a) the priority is on a low number for the line (set it to 1 for your time-table and see if anything changes)
b) you have created a tour, that is connected with a AI-vehicles group like buses or whatever you have assigned in your Ailist.cfg
c) the trips take place on the day you drive them in OMSI (don't hit me, I am just asking...)
4. You have a correct HOF-file for your map, haven't you?
These are the mistakes I had to deal with in the past. Perhaps it's one of them in your case. Good luck!