...These days, I am reluctant to leave my seat. I will do so for a couple of minutes to visit the loo (though even there I'll tend to wait to virtually the end of the journey in case I loose my seat, and I'll take my personal stuff with me; much of that comes from travelling alone, with the rest of it being from knowing some of what goes on, having seen the aftermath of someone having their bag taken off at an intermediate station without their knowledge, and from concern of not being able to get seated again.
Taken off without their knowledge??? Do you mean stolen? But your phrasing suggests some sort of official 'taking off'?
It was probably a theft, but I make no assumption of that - certainly not official in that the removal of the back was news to the train manager who got called. I have come across instances (airline) where an incorrect bag has been picked up from a carousel ... I should not tell you about customer(s) arriving with us in Melksham having flown into the
UK▸ , opening bags and saying "oops - not my stuff" ...