Max startup current for Vacuum cleaner motor
so is this the inrush current of this motor?


YES  300% of the rated current is common for start surge of a low-efficiency motor.  (high-efficiency BLDC motors use 10x to 12x rated current for start surge)


  I need the causes, and if possible I want to know what is the proper way to solve this problem? Is it good to use soft starter?


You may have damaged the motor by excessive winding temp rise from lack of airflow with your design of the vacuum former.  So a soft start may only extend the start duration and allow the blocked airflow temperature to rise faster. 

A blocked vacuum motor uses more than rated current.

However, using a variac or relay controlled autotransformer can reduce the voltage by 50% and thus current but quadruple the startup time.

Suggestions


The vacuum motor never starts with the full air-flow blocked i.e. full load.
Use a shop vac. drum to contain the vacuum to increase airflow and reduce the load on the motor.
use a vacuum pressure sensor for speed control.
Use a brushless DC vacuum motor with separate forced-air cooling and higher efficiency @ 1kW should be adequate.