When creating a multi-page sequence diagram that includes ellipsis (in this case not on the first page), first page(s) loose the swimlanes. Bug present in version 8022.
The following reproduces the bug:
@startuml
box "Module-1"
participant class_1
end box
box "Module-2"
participant class_2
end box
class_1 -> class_2
class_2 -> class_1
newpage Second Page
class_1 -> class_2
'The following line causes swimlanes on first page to disappear
...
class_2 -> class_1
@enduml
Commenting out the line with ellipsis brings back the swimlanes in first page.
PS: Thanks for this great software.