Steps to Reproduce:

1. Create a structure with a jigsaw block in it
2. Put data in jigsaw block form fields
3. Click done

Then you can either:

1. Save structure with structure block
2. Try to load the structure using a different structure block 

OR

1. Quit and Save out of your world
2. Re-enter the world

Observed Results:

All data put into the jigsaw form fields revert back to default upon relogging into the world or loading the structure with a structure block.

(I also tried to edit the nbt data using NBT Studio and then loading the structure with a structure block and it still reverted the data to default values in Minecraft)

Expected Results:

Jigsaw block saves the data upon relogging and upon generating the structure through a structure block.