My group (Urban Cat Coalition in Milwaukee) has a very similar set up and definitely has to scramble to place the tougher cats or returned cats as well. The number is low (we had 4 returned cats in 2018) and working with with adopters has helped keep a lot cats in homes when the person was considering surrender. In most cases, we can text/email/talk on the phone and suggest options people are willing in try. In a couple tough cases, we've sent a (very experienced!) volunteer to the person's home to meet with them and work with them and the cat.
We do have a couple fosters who are set up with the legitimate cat kennels/condos that we bought from a shelter and can take some of the more difficult cats and keep them separate from others. One foster has room for 8 cats in condos (she holds most of our barn cats before they find homes). That has been extremely helpful in a lot of emergency situations (where someone needs to surrender RIGHT NOW, injured feral cats, etc).
Side note: We also require that fosters start any semi-feral cats (who need socialization) in a large dog kennel and slowly work up to more space over time. We have some great protocol from Cat Town in Oakland on socializing cats that our fosters use.