This sounds like a recurrence of an old problem with the Seamless Pattern template. In the past it generated much forum discussion but few useful images. I thought this was fixed but perhaps not.
Here are some old posts with workarounds and a cleaned-up template.
Beginners' Questions my seamless pattern not working ??
Inkscape.org
i have tried step behaviour as well no change . plz can anyone help
Please share the exact steps you are taking. Specific details will help.
The beast has returned...
This sounds like a recurrence of an old problem with the Seamless Pattern template. In the past it generated much forum discussion but few useful images. I thought this was fixed but perhaps not.
Here are some old posts with workarounds and a cleaned-up template.
https://inkscape.org/forums/beyond/seamless-pattern-template-crashes-inkscape/
https://inkscape.org/forums/beyond/seamless-pattern/
https://inkscape.org/forums/questions/inscape-crashing-when-new-document-from-template-on-mac/