All opinions welcome

I know what it is but would like opinions on the cause. Note the warp in the vinyl siding above the stains.

sorry pic to follow

No pic to see.

h’mm if i could see it maybe it would be better.

Sorry look again.

Efflorescence is caused by salts in the brick coming out during water evaporation.
You have mortar missing in that area.

I would say there is a water intrusion issue.

Need to see the top and how was the roof above that area.
Did they have weeps and a moisture barrier at the lintels and other areas?

Ice damming causing built-up moisture to infiltrate behind siding?

Improper installation of siding, fasteners too tight, causing the siding to buckle (expansion/contraction), allowing moisture to penetrate behind the siding. ???