Keynote Crashing when using Custom Theme

Hi,

I have a custom theme I have saved out, I have installed it on multiple Macbook's ranging from M1 up to M4's all on macOS 15.61 or higher.

On some laptops it works fine, on others Keynote crashes when you try and add a new slide from the slide chooser or change the current slides layout, no clear correlation between the affected laptops.

When keynote crashes the console gets filled with the following message until you force quit Keynote.

#Assert *** Assertion failure #2326: -[TSWPStorage(Enumeration) enumerateRangesForAttributes:inRange:usingBlock:] /Library/Caches/com.apple.xbs/Sources/iWorkDependenciesMacOS/shared/text/TSWPStorage_enumeration.mm:83 Range length must not be zero.

The crashing also carries across between user accounts on the same Mac, always getting the same error.

Any help on this is much appreciated.

Thanks,

James