I am trying to add FlexGridsizers to pane's of a notebook but they always go to the first pane. ... too many _1 _2 _3

See Re: wxPerl: Wx::DatePickerCtrl crashes its sizer? where I say

The two are not unrelated. Naming your variables mainsizer,sizer1,sizer2,button1... is not the best way to keep track of what's what, or what goes where, its easy to get confused

One way of keeping track (what goes where) is naming your sizer/container elements by position, and incorporating the parent/child relationship into the name. Afterwards you incorporate your action elements (text/buttons) and name then by purpose/property/action (email_input/email_text,submit_button,cancel_button... )

This naming problem extends to this

$self = MenuBerekening->new($self);
$self = ToolBerekening->new($self);
$self = NotebookBoven->new($self);
$self = NotebookOnder->new($self);
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along with most of your constructors returning two values

Where your problem lies exactly? Its not worth hunting it down, start new file, one for each package, and start fixing the names, and never reuse $self

Also see Re^3: wxPerl Static Text alignment