Thumbnails not generating

I have taken over management of a site – they have a huge number of PDFs they need better access to. I love that your software just does its thing however we’d like the ‘fancy’ thumbnails and I cant work out why they are not generating. I have tried turning off both jetpack and visual composer, still no joy.

Thanks for the help

best wishes

Lisa

Array
(
[thumber] => Array
(
[gs] =>
[active] => Array
(
[av] => 1
[gs] =>
[imagick] => 1
[thumber-co] =>
)

[width] => 200
[height] => 200
)

[thumber-co] => Array
(
[uid] =>
[secret] =>
[subscription] => Array
(
)

[direct_upload] =>
[mime_types] => Array
(
)

)

[gallery] => Array
(
[columns] => 4
[descriptions] => 1
[fancy] => 1
[order] => ASC
[orderby] => menu_order
[relation] => AND
[limit] => -1
[mime_types] => application,video,text,audio,image
[new_window] => 1
[post_status] => any
[post_type] => attachment
[paginate] =>
[attachment_pg] =>
[skip] => 0
)

[css] => Array
(
[text] =>
)

[meta] => Array
(
[version] => 4.2.6
[items_per_page] => 10
[donate_link] => https://www.paypal.com/cgi-bin/webscr?cmd=_donations&business=EE5LWRLG933EN&lc=US&item_name=Document%20Gallery%20Plugin&item_number=document%2dgallery¤cy_code=USD&bn=PP%2dDonationsBF%3abtn_donateCC_LG%2egif%3aNonHosted
)

[logging] => Array
(
[enabled] =>
[purge_interval] => 7
)

)