There appear to be some merged cells at the far right.
When sorting the entire table is re-arainged based on the chosen column. The merged column cells to the right would not be able to follow their corresponding cells in the sort column. Yes, they are empty, but I don't think the spreadsheet takes that into account.
Anyway, that's my guess. Un-merge those cells, and any other column merged cells in the spreadsheet. Merged row cells should be ok.
Anyway, that's my guess on the matter. It bears out in testing, as I merged some column cells in a spreadsheet that wold sort, and the sort option went away.
If I'd thought it through more I'd have originally said look for merged cells in any column, not just the sort column. Sorry.