Why did Shanghai pay less social security last month?

The reason why Shanghai paid less social security last month is:

1, the social security inquiry system has not been updated, and most companies will pay the social security fees of the current month through local taxes before 15 every month.

2. Social security and medical insurance, which could have been deducted together, were deducted separately from this year, but they were not deducted at the same time in the first month, only to find that Shanghai paid less social security last month.