not necessarily the fixer went bad but maybe you didn't fix LONG ENOUGH.
take a clip of the same film, the leader, and put it in the fixer
and see how long it takes to clear to base ( see through ) 2x that time is your total fix time.
2x the original clear time for UNUSED FIX is the clear time for bad fix
Looks like under fixing to me too. Following jnanian's advice should cure the problem. That said, I would try to get some prints from the first two examples. I really like the effect you got with the top two pictures. For me, it just seems to work for those two shots. It would be very hard to duplicate your results intentionally. Print 'em!!
Of course the light of the Scanner has a very hard time penetrating the underfixed film which produces a variety of funny special effects.
Refix and for the future, take all aspects of the fixing stage (age/exhaustion of chemistry, agitation, temperature control) as seriously as you would take the development stage.
If it is Sabattier, then there is a major issue with light levels handling the film. Refixing will settle the issue. If the rebates do not clear with fresh fix, there is fogging involved.
The fixer mixed properly and not old can do many films in its life. I usually mix a batch and then go through my films with maybe a clip test after 10-15 rolls. I use it until it takes more than 4 minutes to clear the clip.