This happened to me as well. I deployed the linear interpolation formula below in Apps Script and it was working just fine, but then stopped working after a few weeks and now produces the following error: "
Error Unknown function: 'linear_interpolation'." I checked that the script was still deployed and it was so I'm not sure why it stopped working.
When I created a copy of the worksheet, which, when doing so, asked to create a copy of the Apps Script that was deployed in the previous sheet, it was working again in the copy of the sheet.
function LINEAR_INTERPOLATION(x, x25, P25, x75, P75) {
return P25 + ((P75 - P25) / (x75 - x25)) * (x - x25);
}
Anyone else seeing this and any tips on how to prevent or troubleshoot?