groups + qceff probit transform failure

[hkershaw-brown]

I think it could be helpful to add a CAUTION comment here.
Because of the new error check, the interaction between the transformations and the groups can become messy. If it happens and the probit transform fails, then only part of the ensemble may be updated for a certain obs. Because of the cycle SEQUENTIAL_OBS the remaining groups, which could be transformed without issues, are disregarded.

Originally posted by @mgharamti in #794 (comment)