If you are running a late style iPad Pro you should be able to handle .shapr3D Files with a couple of thousand Sketches [i.e., meaning number of Lines, curved or otherwise, in the whole Design]. See:
Older style iPads capable of running S3D will not be able to match this performance.
What size, in MB, is the problem Design?
If you can recollect, did this File take a long time to Save?
If it did this may be the answer.
Be aware that if you consider sending the File, to get help, you may have to use an On-Line Service.
Designs that you can access can be reviewed for the Number of Sketches via:
Goto 
Items > Top left Corner > All Items - Bodies - Sketches - Planes and Axes - Images choose Sketches > Add up the Number of Sketches
It is possible that your project can be recovered using a current model iPad Pro.
The file could be split into parts so that eventually with the appropriate kit it could be reassembled ‘good as new’.
There are a few ways too accomplish this unless it has sensitive content that needs to be kept private:
S3D Team can review problem files, but IIRC, files submitted are those with problems other than being too large for the iPad in use. Problem Designs can be sent to:
However it would be polite to ask first, it is a presently busy time for them getting ready for the iPadOS release.
Alternatively you can PM me attaching the file, or placing it on DropBox or similar and send only the Link? First and foremost please consider preservation of your privacy.
Lastly if it is considered Public Knowledge you could post it in a response to this Thread.