Gatekeeping causes many problems. First of all, there are complaints from transgender people: In the personal story from 2007 (only read if you choose for self-determination) you can read what can happen if treatment is not provided soon enough and how this can put the relationship with a gatekeeper under pressure. Similar situations still exist at the moment, as was shown by several sessions during the FreePATHH, see the FreePATHH website.
If you are more into scientific investigations, read two reports that were published in 2016: one is from Patiëntenorganisatie Transvisie and the other one is from Principle 17. In January 2017 Trans United published an investigation report about bi-cultural transgender people, which also contained complaints about the psychologists.