GuilhemH
Having 0 error for 207/206 of the reference material selections is the expected behavior for the default UComPbine settings because every time-slice of the reference material 207/206 is corrected to the expected value. If you check "Use selection means", this corrects the selection average (rather than each time-slice) to the expected value, so in this case you get some error for each.
Having 0 for other channels (like 207/235) is unexpected and is not what I observe here. If that is the case, please send your io4 file to support for us to investigate.
All the best,