I just figured out the answer to the problem. I just added CancellationToken argument to the functions:
From:
private async Task<IEnumerable<Account>> SearchAcc(string value) {...}
private async Task<IEnumerable<Role>> SearchRole(string value) {...}
To:
private async Task<IEnumerable<Account>> SearchAcc(string value, CancellationToken token) {...}
private async Task<IEnumerable<Role>> SearchRole(string value, CancellationToken token) {...}