This study aimed to explore changes in gambling behaviours and gambling disorder (GD) treatment uptake during the COVID-19 pandemic among those with a heightened vulnerability to gambling-related harm. This was a single-center, cross-sectional, retrospective case series study assessing gambling behaviours and GD counselling participation among a vulnerable population sector following the COVID-19 shutdown. The clinical records of clients at a community substance use disorder (SUD) treatment center were explored (N = 67). Eight clients (n = 8) had satisfied the objective criteria, and were qualified for data exploration and analysis of gambling activities and GD treatment participation following the COVID-19 shutdown. All clients in the study belonged to subgroups at an elevated risk for gambling-related harm, with a mean duration of gambling problems of 9.5 years. Following the COVID-19 shutdown, an increase in gambling activities was noted in five cases. Migration to online gambling was noted in three cases. In two cases, no change in gambling activities was noted, and a reduction of gambling activities was noted in one case. In seven cases, no screening for gambling problems prior to current SUD program was noted. None had a history of, nor were currently engaged in counselling for gambling problems. The COVID-19 crisis and associated increase in gambling participation, coupled with a diminutive gambling counselling uptake during the pandemic, present an opportunity to rethink current behavioural addictions service delivery model for those with an increased vulnerability to gambling-related harm. Further investigation of the changes in gambling participation, and a closer look at optimizing GD service delivery among vulnerable population sectors during the COVID-19 crisis is warranted.