On this forum, there's a long-standing thread,
Anyone else been stuck in Quality Check for a week or more?, but that thread discussed the MINI Cooper SE cars stuck at Plant Oxford in the UK. The consensus in that thread was that a single missing part could be responsible for pulling a car from the production line to the sideline. The group who found themselves united by this dilemma eventually saw the factory release all of their SEs from QC within the span of a week or so, but that week didn't happen until the production line was paused for other reasons.
Hopefully, the part your Countryman needs won't be long in coming and the factory will move it back to the production line quickly.