I don't think the bill requires the server side to be open source. I think it is sufficient as long as the client side can use libre software to interact with t

I don't think the bill requires the server side to be open source. I think it is sufficient as long as the client side can use libre software to interact with the government. (But this is not explicitly stated in any of the links I followed.) Another comment mentions fillable PDFs not working in non-Adobe software. This seems like the most likely culprit to me. And in general, if someone has to go back over the entire surface area of an application and re-test everything to find all the quirks like this, I can start to understand how that huge cost estimate might make sense.