Ive created a magazine layout with images that span across two pages. When I export, there is a large white margin in the centre of the spine and the pages seem to be doubling up in the centre. I've never had this issue before and have no idea how to fix it. The magazine is 30 pages and will be saddle stitch so there shouldn't be a large margin for the spine.
Does your printer ask for spreads? Usually, they ask for single pages.
What you are seeing is the result of including an inside bleed on facing pages (the inside bleed area is taken from the opposite page) and the printers marks and exporting (or possibly just viewing) as spreads.
You should export as single pagers so the perinter can impose the pages on the size sheet that will be used on the press. You may or may not actually need the inside bleed (which is a question to ask the printer). The printer will impose the pages and use only as much of the inside bleed as required for creep, so thata is not a problem, but there is a problem with your page count -- saddle stitched publications must have a multiple of 4 pages including the covers. Also, you need to increase the offset for your marks to be at least equal to the bleed allowance so they don't appear inside the bleed area.
your bleed is on all sides of the page. Therefore you see it on all sides of a page in your PDF.
That is no issue at all, because nowadays a printing company only relies on the relevant PDF boxes like e.g. bleed and trim. The printer's imposition software for saddle stitch binding should be able to do it right.
Follow the advice of your printer regarding bleed settings.
Could also be that you need no crop or bleed marks in the PDF.
( Adobe Community Professional )