There are many possible reasons for that.
Regarding the sudden cessation of contrails, it could be that the aircraft was in descent or climb out of the narrow altitude band conducive to contrail formation.
Other reasons are passage through an air mass boundary, for example, crossing a jet stream axis or a frontal passage aloft.
As for the different shutoff of the contrails for the two engines - one engine was operating at a slightly higher temperature than the other, so that the exhausting H2O/CO2 condensate have a slightly different cooling rate.
Or you can believe that it’s the government trying to poison us all in a conspiracy with Big Tech, Big Pharma, and Trump.
Seems to me the contrail would taper off and not shut off like that. The quick shut-off seems artificial.