Not a citation and not a proof, just pointing out an additional group - there is a whole class of mental problems that can lead one to poverty and keep them there. They often need money and stable situation (have time to visit a doctor, have money to buy drugs OR have a job to have an insurance to get drugs) to be kept at bay, and if they force you into bad situation it becomes very hard to get out of it.
Some people are employable only because huge inefficiencies that exist in job market (e.g. it's easy to pass a programming test and hard for your employer to determine your actual productivity) and that would be better off on an UBI, providing some value without the stresses of not getting paid for being unable to e.g. maintain 9-5 schedule, or your employer not understanding that you have random periods of downtime due to depression.
Some people are employable only because huge inefficiencies that exist in job market (e.g. it's easy to pass a programming test and hard for your employer to determine your actual productivity) and that would be better off on an UBI, providing some value without the stresses of not getting paid for being unable to e.g. maintain 9-5 schedule, or your employer not understanding that you have random periods of downtime due to depression.