is there a bug in the virus definition because on 24-10-2021 the total is 28,558,889 while at this time the definition of 8-11-2021 only becomes 28,522,075 ?
No.
There are updates and optimisations to the Virus Definitions. Many individual signatures can be optimised to detect more than one virus signature. On some big ones in the past have resulted in a much lager change than this,
Optimised virus signatures should speed things up.