We did not have any issues getting on board. We arrived to take a ferry to Gozo on 28th around 10:00 and had to wait around 1.5 hours. On the way back on 31st we had to wait around 1 hour.
However, as far as we heard one might experienced longer waiting times sometimes, around 3-4 hours. This may be influenced by weather conditions or technical issues on ferries.
Credit:stackoverflow.com‘