I had the problem of numbers crashing down every time I wanted to keep working with a previously made spreadsheet. The fact is that that was the only spreadsheed that would crash when trying to edit it and indeed, it is the assistance template.
I had made more sheets from zero and those ones remained unaffected. Reinstalling the app did not work and it kept collapsing, so I came up with the idea of duplicating the problematic sheet and erase the original one and it just worked. I can now keep working with my data without crash. I hope this helps to guide anybody who might have the same problem as I did, fortunately the issue didn't get bigger just affecting one spreadsheet.
Hope you have luck people and that Apple faces its issues, for we have paid for this apps and they just MUST.