We can point to several factors for the increase in vacancies. It could, for example, be due to a rapid reopening of an industry where there's an adjustment period required for matches to be made between available workers and vacancies. It may be an indication of normal economic activity where there's turnover and transition within an industry. In some cases it may be a shortage, either an absolute shortage, or some type of mismatch between the working conditions associated with the job and the willingness of available workers to take those jobs. As well there are geographic imbalances, so that there may not be a shortage, but there may be an imbalance between where available workers are located and where the vacancies are located.
There are many factors and it's important to interpret vacancies within a specific industry and occupation in the context of a broader set of labour market and economic indicators.