We resolved this problem by removing the bidirectional relation in the DTOs (removing the BusTypeDto from the SeatDto) and also using the ToList method before the mapping (it wasn't required before).
Anyone to help Do i need to use interceptors to resolve this problem? which method on which class?
so multitenancy is mainly (or even completely i guess) used for SAAS? i had it all wrong. I'll use roles/permissions as you've suggested, and affect them to my users.
Thanks for the answer ;)
BTW, CurrentSession is the name of the injected IAbpSession property in both the AbpController based controllers and ApplicationService based services if anyone needs it